Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We report on ultrasound measurements in a single crystal of the antiferromagnet U₂Rh₂Sn as a function of temperature and magnetic field. We find pronounced anomalies in the sound velocity at the Néel temperature, 25 K, and at the field-induced spin-flop-like transition at 22.5 T, which points to a strong magnetoelastic coupling. Additionally, we find that in the paramagnetic regime the temperature dependence of the magnetic susceptibility and the field dependences of the magnetization and sound velocity of transverse acoustic waves can be well described assuming a localized character of the 5 f electrons. Using this premise, the crystal-electric-field scheme of U₂Rh₂Sn has been determined.

Magnetic properties and magnetic structures of layered GdMnSi₂ compound were studied using quasisingle crystal, high magnetic fields up to 520 kOe, and neutron powder diffraction experiment designed for high absorbent systems. It was shown that GdMn₂Si₂ has strong easy plane type magnetic anisotropy at temperatures T_Gd < 52 K at which Gd atoms are magnetically ordered. At temperatures 52 K < T < 453 K, the compound has antiferromagnetic ordering of Mn layers and easy axis type magnetic anisotropy with the easy axis directed along the tetragonal c-axis. The exchange-induced in-plane magnetic anisotropy of layered GdMn₂Si₂ at low temperatures arises to prevent magnetic frustration in Gd layers. Magnetic properties of GdMn₂Si₂ at temperatures below 52 K can be described within a threesublattice model based on the Yafet-Kittel approximation.

Wayforlight.eu is the gateway to finding the most suitable instruments for experiments with synchrotron, FEL, and laser light sources. The portal's main asset is a detailed searchable catalogue of facilities, beamlines, and instrumentation available at European light sources. Thanks to its advanced search tools, a visitor can filter beamlines by scientific discipline, by technique, but also by energy range or sample type.

New experimental methods for synthesis of low dimensional carbon structures still attract considerable attention, many of them based on catalytically driven processes.
In this contribution we present REELS and Auger spectroscopy study of Ni-induced
layer exchange in Ni/C-bilayer thin film system. EELS spectroscopy in reflected
mode (REELS) and Auger electron spectroscopy (AES) were employed to characterize
the structure, homogeneity and quality of carbon and nickel film (each having
thickness around 50 nm) and their interface between, before and after thermal annealing
at 700 °C. AES mapping and depth profiling revealed a layer exchange
between the layers after thermal annealing, accompanied by partial nickel diffusion
into MgO substrate. REELS analysis showed successful structural transformation
of initially amorphous carbon layer into compact graphitic one. The transformed carbon
layer has a slightly rippled surface as confirmed by topological backscattered
electron imaging.

The graphitization of amorphous carbon in thin film stacks with Ni was investigated in situ as a function of the initial stacking order, temperature and time by Rutherford backscattering spectrometry and Raman spectroscopy. Four different bilayer and triple layer stacks were exposed to heating ramps up to 700 °C. The graphitization occurred simultaneously with a layer exchange (LE) and was completed during the applied heating ramp. The temperature-resolved measurements allowed the determination of the onset temperatures and transition rates for the respective stacking order. Finally, the activation energies for the graphitization of the amorphous carbon were estimated for both LE directions. In combination with thermodynamic calculations,
this in situ study allowed to identify metal-induced crystallization with LE via wetting and diffusion along grain boundaries as mechanism responsible for the graphitization of amorphous carbon thin films in contact with Ni, instead of bulk dissolution/precipitation. The proposed model can potentially be used to estimate the catalytic transformation of group 14 elements in contact with transition metals.

Two types of ions (fluorine and titanium) are implanted into films of regio-regular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) spin-coated on glass substrates with subsequent annealing in argon atmosphere to modify their electrical properties and structure. The ion energy and fluence were within 0.2–40 keV and 10¹³–10¹⁵ cm⁻² respectively. The dc resistance enhances after the intensive ion beam treatment while the ac impedance decreases. Ti ion implantation with 40 keV energy and 10¹⁴ cm⁻² fluence induces decrease of the ac impedance by almost two orders of magnitude and appearance of the molecular hydrogen features in ¹H NMR spectrum. The UV–VIS spectra of the films are blue shifted after their exposal to the ion beams, which correlates with the presence of oxygen. The ratio of the oxygen to carbon peak intensities (O1s/C1s) in the XPS spectra is proposed as a measure for the local partial disturbance of the film. EPR spectra demonstrate formation of the paramagnetic states with g factor <2, which is accompanied with the down-field shift of the NMR spectrum. The ion beams are found to have no significant etching effect as per results of the film thickness measurements and AFM images.

The catalytic graphitization with layer exchange (LE) of amorphous carbon in thin film stacks with Ni was investigated as a function of the initial stacking order. Bilayer and triple layer stacks were exposed to heating ramps up to 700 °C. Raman spectroscopy showed the formation of a layered graphitic structure after the annealing.
During outwards LE, as C is transported towards the sample surface, a smooth layer with graphitic planes parallel to the interface with the substrate has formed through a 2D growth. A significant restructuring of the Ni layer appeared during inwards LE, as C is transported towards the substrate. Here, the fragmentation of the Ni layer, as well as the regions with turbulence-like and folding defects indicated a 3D growth.
The degree of LE, quantified by ion beam analysis, is 95 % and 80 % for the outand inwards direction, respectively. Based on the calculation of surface and interface energies of the initial and final states, thermodynamic estimations pointed to the wetting of Ni grain boundaries by C atoms as the initial driving force for the LE and allowed a consistent understanding of the LE directionality and of the final thin film microstructure.

One of the fascinating qualities of spin waves (or magnons), which are the elementary excitations in magnetically ordered substances, is their nonlinear behavior at moder- ate excitation powers. This makes spin waves not only an attractive model system to study general nonlinear systems, but it also provides a way to utilize nonlinear dynamics in possible technical applications. In a ferromagnetic nano disk which is magnetized in the vortex state, the spin-wave modes meet strict boundary conditions and therefore inherit a discrete spectrum. When driven with a large enough excitation field, they can decay into other spin-wave modes within well-defined channels due to a nonlinear process called three-magnon scattering [1]. The aim of this project is to explore this phenomenon within nonlinear spin-wave theory and by means of micromagnetic simulations.
For this purpose, first the linear dynamics are mapped out and the possible scattering channels are predicted. The stability of these channels with respect to static external fields is studied. Within this context, exotic spin-wave modes which arise in a broken cylindrical symmetry are found. Moreover, a model to predict the temporal evolution of the spin-wave modes is developed within the classical Hamiltonian formalism for nonlinear spin-wave dynamics. Together with micromagnetic simulations, this model is applied in order to study the power-dependence of three-magnon scattering as well as to uncover a phenomenon called stimulated three-magnon scattering, which may allow for an integration of this nonlinear pro- cess in magnonics circuits. The results are compared with Brillouin light-scattering experiments which were conducted prior to this thesis or were motivated by it. Financial support of within DFG programme SCHU 2922/1-1 and KA 5069/1-1 is acknowledged.

In this talk I will make a brief overview of our activities for integration of different 1D and 2D materials into functional structures and devices.

I will first present the work on fabrication, processing and application of group IV semiconductor nanowires (NWs). These include top-down fabricated Si, SiGe and Ge NWs as well as bottom-up grown Si, Ge1-xSnx with x = 0.07-0.1 and GaAs/In0.45Ga0.55As NWs. I will also consider the innovative devices that we are targeting: junctionless nanowire transistors (JNTs), reconfigurable field effect transistors (RFETs) and band-to-band tunnel FETs (TFETs).

I will next discuss our activities for fabrication and characterisation of FETs based on 2D heterostructures. As examples I will show FETs fabricated on hBN-encapsulated InSe, a material with attractive properties but very unstable in ambient atmosphere, as well as TFETs fabricated on hBN/MoS2/WSe2/graphene heterostructures.

Finally, I will pay some attention to our work on using DNA origami templates for the fabrication of functional structures with the outlook to the application of DNA origami for self-assembly of electronic circuits. In particular, I will show fabrication of conducting metallic NWs using templates of DNA nanotubes, nanosheets and nanomoulds as well as incorporation into them of molecules and semiconducting nanoparticles for enhanced electronic functionality.

Germanium (Ge) is a promising high mobility channel material for future nanoelectronics. Materials with high carrier mobility can enable increased integrated circuit functionality or reduced power consumption. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics [1].

The introduction of impurity atoms allows the tuning of the electrical properties of the semiconductor material. Ion beam implantation is an industrial standard for semiconductor's doping as it can incorporate single ion species with a single energy in a highly controlled fashion. However, the destructive nature of ion beam implantation requires a crystal recovery step such as an annealing process [2].

In this work, Germanium-on-insulator (GeOI) substrates were doped with phosphorous (P) using ion beam implantation followed by flash lamp annealing (FLA). During FLA process the implanted layer recrystallized and P was electrically activated. Then Ge nanowires were fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Raman spectra showed the amorphisation of Ge structure after implantation and good recovery after FLA (Fig. 1). Rutherford backscattering spectrometry (RBS) measurement in random (R) and channeling (C) modes (Fig. 2) were used to verify the crystal quality of Ge layer before and after FLA. As one can see, the yield intensity of the channeling mode was increased after implantation, which can be related to amorphisation of the top Ge layer. Also, the yield peak of flashed GeOI has a good match with unimplanted counterpart, which shows the good recrystallization during FLA. Moreover, we designed Hall effect measurement configuration for single Ge nanowires (Fig. 3) to determine the carrier mobility and carrier concentration. The results of these measurements will be shown at the conference [3,4]. The goal is to fabricate p-n junction along the Ge nanowires and use it as an infrared sensor.

Germanium (Ge) is a promising high mobility channel material for future nanoelectronic devices with a lower effective charge carrier mass than Silicon (Si) and higher electron and hole mobility. Materials with high carrier mobility can enable increased integrated circuit functionality. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics. In this work, Ge nanowires were fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Then ion beam implantation was used to introduce phosphorous (P) dopant atoms into the Ge nanowires. Afterwards, flash lamp annealing (FLA) was applied to recover the crystal structure of the Ge nanowires and activate the dopant atoms. Micro-Raman spectroscopy spectra showed that by increasing the fluence of ion implantation, the peak of optical phonon mode in Ge was broadened asymmetrically which shows that dopant atoms are electrically activated. Moreover, we are designing Hall Effect measurement configurations for single Ge nanowires to determine their mobility and carrier concentrations.

This paper reports on the results of Er+ ion implantation into various ZnO structures - standard single crystal c-plane (0001) ZnO, nanostructured thin films and nanorods. Er+ ions were implanted using an ion implantation energy of 400 keV and implantation fluences in the range of 5×1014 to 5×1015 ions/cm2. Er concentration depth profiles and the degree of crystal damage were measured using Rutherford backscattering spectrometry (RBS) and RBS/channelling (RBS/C). Additionally, Raman spectroscopy was used to analyse structural modifications of the prepared samples. The main focus was placed on the luminescence properties of various ZnO structures. The results showed that the characteristic bands of ZnO, i.e. near-band-edge (NBE) luminescence and deep-level emission (DLE) - that can be influenced by the excitation wavelength - appeared in the spectra of single crystals and nanorods. The characteristic luminescence bands of erbium ions in the NIR region appeared in ZnO single-crystal samples and nano-crystalline films.

Germanium (Ge) is a promising high mobility channel material for future nanoelectronic devices with a lower effective charge carrier mass than Silicon (Si), which results in a higher electron (×2) and hole (×4) mobility. Materials with high carrier mobility can enable increased integrated circuit functionality or reduced power consumption. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics. Doping or the introduction of impurity atoms allows the tuning of the electrical properties of the semiconductor material. Ion beam implantation is an industrial standard for semiconductor's doping as it can incorporate single ion species with a single energy in a highly controlled fashion. The destructive nature of ion implantation doping due to the deposited energy and resultant cascade of recoils within the nanowire volume requires a crystal recovery step such as an annealing process. In this work, Ge nanowires were first fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Then ion beam implantation was used to introduce phosphorous (P) dopant atoms into Ge nanowires. Afterwards, flash lamp annealing (FLA) was applied to recover the crystal structure of Ge nanowires and activate the dopant atoms. Micro-Raman spectroscopy spectra showed that, by increasing the fluency of ion implantation, the optical phonon mode of Ge peak was broadened asymmetrically. This is related to the Fano effect and shows that dopant atoms are placed in substitutional positions and are electrically activated. Moreover, we are designing three- and four-probe Hall Effect measurement configurations for single Ge nanowires to determine their mobility and carrier concentrations.

As high power laser systems producing high repetition rate pulses become interesting for applications in e.g.
radiation therapy, there is a high demand for rapid and controlled target delivery at the high power laser focus.
Due to their continuous and debris-free operation, cryogenic target systems producing renewable jets of
hydrogen [1] or other species proved to be very beneficial. Furthermore, the low plasma density of solid single
species hydrogen of only 30nc@800nm and the availability of different jet geometries allowed for gaining
deeper understanding of the laser proton acceleration process [2,3,4]. In this talk we focus on the
implementation of a hydrogen jet target at the Petawatt (PW) beam line of the high power laser source DRACO
at HZDR. The laser system delivers pulses with energies of up to 23J and pulse durations of about 30 fs on
target. We present significant improvements of the operation robustness of the cryogenic target with respect to
the harsh environment around the interaction zone and thereby leading to substantial increase in stability of the
laser accelerated proton beams. Prior and during experiments, characterization of the jet target was conducted
with a synchronized off-harmonic optical probe laser. It allowed for on-shot study of the onset of ionization
induced by the leading edge of the main laser pulse prior to its intensity maximum with sub-picosecond time
resolution. Also, by adding artificial pre-pulses the initial shape and size of the target can be engineered for
optimal interaction conditions with the high intensity laser pulse.

The probabilities of various elementary laser/photon/electron/positron interactions display in selected phase space and parameter regions typical nonperturbative dependencies such as proportional to P exp{/aE(crit)/E}, where P is a preexponential factor, E-crit denotes the critical Sauter/Schwinger field strength, and E characterizes the (laser) field strength. While the Schwinger process with a = a(S) pi and the nonlinear Breit/Wheeler process in the tunneling regime with a = a(nlBW) 4m/3 omega' (with omega' the probe photon energy and m the electron/positron mass) are famous results, we point out here that also the nonlinear Compton scattering exhibits a similar behavior when focusing on high harmonics. Using a suitable cutoff c > 0, the factor a becomes a = a(nlC) 2/3 cm/(p(0) + root p(0)(2) / m(2)). This opens the avenue toward a new signature of the boiling point of the vacuum even for field strengths E below E-crit by employing a high electron beam/energy p(0) to counter balance the large ratio E-crit/E by a small factor a to achieve E/a -> E-crit. In the weak/field regime, the cutoff facilitates a threshold leading to multiphoton signatures showing up in the total cross section at subthreshold energies.

Beam-driven plasma wakefield accelerators (PWFAs) offer a unique regime for the generation and acceleration of high-quality electron beams to multi-GeV energies. Here we present an innovative hybrid staging approach, deploying electron beams generated in a laser-driven wakefield accelerator(LWFA) as drivers for a PWFA, integrated in a particularly compact setup. This scenario exploits the capability of LWFAs to deliver shortest, high peak-current electron bunches [1] with the prospects for high-quality witness beam generation in PWFAs [2]. The feasibility of the concept is presented through exemplary particle-in-cell simulations, before describing experimental results from extensive campaigns performed at high-power laser facilities; ATLAS (LMU, Munich), SALLE-JAUNE (LOA, Paris) and DRACO (HZDR, Dresden). Using few-cycle optical probing we captured clear images of beam-driven plasma waves in a dedicated plasma stage, allowing us to identify a non-linear plasma-wave excitation regime. Trailing the plasma waves, the impact of ion motion to the transverse modulation of the plasma density was observed over many picoseconds [3]. Furthermore, we demonstrate for the first time the acceleration of distinct witness beams in such LWFA-driven PWFA (LPWFA) setup, showcasing an accelerating gradient on the order of 100 GV/m. These milestones pave the way towards compact sources of energetic ultra-high brightness electron beams as well as a miniature model for large scale PWFA facilities.

We investigate the magnetic field dependence of the spin excitation spectra of the chiral soliton lattice (CSL) in the helimagnet CrNb₃S₆, by means of microwave resonance spectroscopy. The CSL is a prototype of a noncollinear spin system that forms periodically over a macroscopic length scale. Following the field initialisation of the CSL, we found three collective resonance modes over an exceptionally wide frequency range. With further reducing the magnetic field towards 0 T, the spectral weight of these collective modes was disrupted by the emergence of additional resonances whose Kittel-like field dependence was linked to coexisting field polarised magnetic domains. The collective behaviour at a macroscopic level was only recovered upon reaching the helical magnetic state at 0 T. The magnetic history of this non collinear spin system can be utilized to control microwave absorption, with potential use in magnon driven devices.

The coupling between high power laser-driven plasmas physics, atomic physics and nuclear physics aiming to detect and study NEEC/NNET is a very interesting and exciting research area. In this talk, we propose to study NEET/NEEC in buried layer targets, using high repetition-rate (1-10 Hz) 100 TW to PW class laser systems. In this scenario, extreme conditions of highly charged ions with ~ keV temperature at solid density are predicted by our Particle-In-Cell (PIC) simulations (including both collisions and ionization) enabling the study of NEET/NEEC in buried layers [1]. The simulations show that the expansion/compression waves are launched at layer interfaces due to Gigabar electron pressure gradients caused by return current heating. The hydro-motion pushed by the expansion/compression waves is rapidly converted into thermal motion mainly due to the efficient ion-ion collisional coupling, leading to the extreme temperatures at about solid density. The experimental feasibility to realize NEET/NEEC at the HZDR DRACO laser and the HiBEF laser at EuXFEL will be discussed [2].
[1] L. G. Huang, M. Bussmann, T. Kluge, A. L. Lei, W. Yu, and T. E. Cowan, Phys. Plasmas 20, 093109 (2013).
[2] http://www.hibef.eu.

Demanding applications like radiation therapy of cancer have pushed the development of laser proton accelerators and defined necessary proton beam properties as well as levels of control and stability.
The presentation will give an overview of the recent experiments for laser driven proton acceleration employing a cryogenic target system which is capable of producing a renewable and debris free jet target. The micrometer sized pure hydrogen jet is characterized by a low plasma density of 30 times the critical density at 800 nm and was irradiated at the Petawatt (PW) amplifier stage of the high power laser source DRACO at the HZDR. The Ti:sapphire system delivers laser pulses with energies of up to 23 J and pulse durations of 30 fs on target.
In this talk we present substantially improvements of the target system leading to an increase in stability of the accelerated protons as well as the long-term operations. Evaluation of different target geometries (cylindrical with a diameter of 5µm and planar with up to 4x20 µm²) demonstrating the capabilities in terms of size and shape of available hydrogen jets.
We report on the laser contrast dependencies of the proton beam properties by introducing artificial pre-pulses and describe their influence on the target shape at the interaction time by using a synchronized optical probe beam.
Furthermore different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane from the jet target, reaching foil-like proton cut-off energies in target normal direction.

In this talk, we will firstly present a systematic study of the bulk magnetic field generation using particle-in-cell simulations, that we observe the effect of varying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, target thickness and material, and experimental geometry. The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The simulations have also shown that the collisional ionization potential and model are critical to determining the structure and diffusion time of the self-generated magnetic fields. Then we will propose to probe the bulk magnetic fields inside the solid density plasmas by X-Ray polarimetry via Faraday rotation using an X-Ray free electron lasers (XFEL), taking its advantage of simultaneous high spatial-temporal resolution and several tens of micrometers attenuation length in solid. The synthetic simulations predict that the XFEL polarization is rotated by a few hundred micro-radians after penetrating through solid density plasmas which is feasible to be measured with X-Ray polarimetry.
With the results of this work, we are in an excellent position to maximize our chances of measuring laser generated magnetic fields using Faraday rotation at high power laser beamlines at XFELs. One of the first examples of this will be at the European XFEL-HED endstation, in the frame of Helmholtz International Beamline for Extreme Fields at the European XFEL (HiBEF) project, where a 7.5J/300TW high power laser has already installed as a permanent instrument. A dedicated beamtime at the European XFEL-HED endstation to investigate the performance of ultra-high purity X-ray polarimeters under the conditions of European XFEL source has already been scheduled in the end of May, 2019. This is expected to become the basis to probe the laser-driven ultra-strong magnetic fields inside the solid-density targets, accessed via plasma Faraday rotation and imaging polarimetry.

The integrated flow of primary and secondary resources in the loop is in the centre of the Circular Economy (CE) paradigm. To optimize the use of resources, a system-wide thinking, which links the primary and secondary production of the whole processing chain, is required. Digitalization and process simulation enable the linking of these relevant aspects together, optimising the resource use and minimising the environmental impact.

Aluminium’s reactivity poses a challenge for resource efficient recycling. In the re-melting of Al scrap, most of the impurities remain in the molten aluminium. This emphasizes the importance of the quality of the scrap in preventing contamination and reducing the need for dilution with primary aluminium in the alloying phase.

This paper analyses an aluminium recycling flowsheet that combines detailed physical separation models with re-melting and alloy production. The simulation model captures the impact feed quality and the efficiency of the physical separation stage have on specific alloy production. Optimum strategies for alloy production can be found for each specific feed type to minimise resource consumption. The paper demonstrates how digitalization allows more precise and efficient use of finite resources in the sense of CE.

A combination of density functional theory (DFT) and an efficient calculation method based on Atomistic Kinetic Monte Carlo simulations (AKMC) is used to investigate the interdependence of oxygen (O) and vacancy (v) diffusion in bcc Fe and in dilute iron alloys with the substitutional atoms Y and Ti. Both O and v are considered as mobile while the substitutional atoms are assumed to be immobile. DFT is applied to determine the binding energy between O and v for different distances, the migration barriers for O in the environment of v, and the corresponding barriers of v in the vicinity of O. In agreement with previous work O and v have a very strong binding at the 1st neighbor distance. On the other hand, the calculations show that the Ov pair at the 6th neighbor distance is instable. The newly found simultaneous jumps of both O and v compensate the lack of jump paths that would occur due to this instability. The DFT results are employed to determine the diffusion coefficient of O and v using the AKMC-based calculation method. At first a model system with fixed O and v concentrations is studied. It is found that even a small v content of some ppm can lead to a strong reduction of the O diffusivity. A similar effect is obtained for v diffusion under the influence of O. Furthermore, investigations on the interdependence of O and v diffusion in the first phase of thermal processing of oxide dispersion strengthened iron alloys are performed, and the influence of the substitutional atoms Y and Ti is studied. A simple thermodynamic model is employed to determine the concentration of O, Y, and Ti monomers as well as the total v concentration, for a typical total content of O, Y, and Ti. These results are used in calculations of the diffusion coefficients of O and v. Not only a strong mutual dependence but also a significant influence of Y on O diffusion is found. Finally, O and v diffusivities in a system with an O content close to the thermal solubility are calculated, where the monomer and total concentrations are determined by two different thermodynamic models. Even for such a low amount of O in the alloy the diffusion coefficients differ strongly from those in perfect bcc Fe.

The optimization for an upscaled technical production of a lower rim-functionalized p-tert-butylcalix[4]arene, furnished with N₄O₄-donor ligands for superior solvent extraction separation between heavy and light lanthanides, is described. We demonstrate that reducing the polarity of the aprotic solvent in the (1,3)-distal esterification of p-tert-butylcalix[4]arene 1 does not compromise the quality or yield of product 2. It was possible to use the technical quality educt 1, that is, without prior crystallization in toluene, in conjunction with reductions in reaction time and solvent volume. The raw diester product 2 could be used, without prior recrystallization (which originally required 3 days) in the condensation reaction with hydrazine monohydrate to form hydrazide 3. Most importantly, the solvent volume required in the final condensation reaction of 3 with 8- hydroxyquinoline-2-carboxaldehyde could be reduced by an order of magnitude by using chloroform. Not only was the final disubstituted product yield improved but also the purity of the final product could be ensured by preventing the precipitation of the intermediate monosubstituted product during reaction. The filtration characteristics of the final product, as well as its solvation properties during solvent extraction of lanthanides were significantly improved.

Johann Wolfgang von Goethe is known the world over as a renowned writer. However, he was also involved in scientific studies and has written several scientific books, of which he considered the “Theory of colours” (“Farbenlehre”, 1400 pages published in 1810) his most important work overall. In this work, he characterises colours as arising from the interplay between light and dark. This is in contrast to Newton’s analytical treatment of colour from one century earlier, which is based on the observation that white light can be separated into colours with a prism, that Goethe opposed. Over the centuries, Goethe’s theory was discredited and Newton’s theory prevailed. However, Goethe performed systematic and accurate optical measurements.
For these experiments, he and his partner J. Ritter, who discovered UV-light, used water prisms and glass prisms ordered from a glassmaker in Jena. The aim of current research is to reconstruct these optical experiments and the observed spectra [1]. For this, detailed knowledge of the composition of the glass prisms is important. This knowledge is, for example, also important to evaluate how innovative his prisms were.
Therefore, eleven prisms from Goethe’s estate or from contemporary sources belonging to the Klassik Stiftung Weimar have been analysed at the external beam setup of the Ion Beam Center at the HZDR. A 4 MeV proton beam has been used to acquire PIXE, PIGE and RBS spectra, sometimes on several areas. Care had to be taken to minimise damage by using short measurement times and measuring on inconspicuous areas because the glass quickly showed dark spots under irradiation. The PIXE and PIGE spectra have been used for quantitative analysis in an iterative procedure and the RBS spectra have only been evaluated quantitatively. The results of this analysis and the interpretation are presented in this work.

Junctionless nanowire transistors (JNTs) are gated resistors where the source, channel and drain have the same type of doping without any dopant concentration gradient. The JNT is the simplest transistor structure possible and probably the most scalable of all field effect transistor (FET) structures. It is easier to fabricate than standard metal-oxide-semiconductor FETs (MOSFETs) and has also a number of performance advantages over them. [1, 2, 3] Two of the advantages are especially important for the JNT application as sensors:

1. The current flow in JNTs is not controlled by a reverse biased p-n junction as in standard MOSFETs but entirely by the gate potential. Therefore, they are more sensitive to any change in the electrostatic potential on the channel surface acting as a gate potential.

2. JNTs demonstrate bulk conductance near the centre of the channel, in contrast to the conductance in a thin surface inversion or accumulation layer near the gate in the inversion mode or accumulation mode MOSFETs, which leads to higher drive currents. Moreover, this fact makes the conduction in JNTs less affected by the noise-inducing parasitic surface states than in the case of conventional MOSFETs, which is very important for achieving high signal-to-noise ratio and low detection limit.

In the presentation, these advantages will be discussed in detail followed by results of implementation of silicon (Si) JNTs as chemical and biological sensors. A series of experiments for sensing the ionic strength and the pH value of buffer solutions have proven the excellent sensitivity of these sensors. [4, 5] Moreover, sensing of the protein streptavidin at a concentration as low as 580 zM has been observed, which is by far the lowest concentration of this protein ever detected and corresponds to detection in the range of only few molecules.

The high sensitivity of JNT sensors, combined with their very simple structure and relaxed fabrication process, makes them promising candidates for cheap mass production by the conventional microelectronic technology. This can enable their numerous applications in various fields where fast, low-cost, label-free, low-volume and real-time detection of chemical and biological species at low detection levels is required.

REFERENCES:

[1]. J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nanowire transistors without junctions. Nature Nanotech. 5, 225 (2010).
[2]. J. P. Colinge, C. W. Lee, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, A. Kranti, R. Yu. Junctionless Transistors: Physics and Properties, in Semiconductor-On-Insulator Materials for Nanoelectronics Applications. (Eds: A. Nazarov, J. P. Colinge, F. Balestra, J.-P. Raskin, F. Gamiz, V. S. Lysenko), Springer-Verlag Berlin, Heidelberg, Germany, pp.187-200, Ch. 10 (2011).
[3]. J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Junctionless Nanowire Transistor (JNT): Properties and design guidelines. Solid State Electron. 65-66, 33 (2011).
[4]. Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices. Microelectron. Eng. 118, 47 (2014).
[5]. Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, In "Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting", (Eds: A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre), Springer International Publishing AG, Cham, Switzerland, pp. 367-388, Ch. 17 (2014).

Junctionless nanowire transistors (JNTs) have been recently proposed as a disruptive alternative of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. They are gated resistors where the source, channel and drain have the same type of doping without any junctions and dopant concentration gradient. Thus JNT is the simplest possible transistor structure and probably the most scalable of all FET structures. It is easier to fabricate than standard MOSFETs and has also a number of performance advantages over them [1,2]. Therefore, JNTs have quickly attracted a vast interest. However, their application as sensors, although very appealing, has not yet been extensively studied.

Here we report on the fabrication of silicon JNTs and their implementation as chemical and biological sensors. The devices have been fabricated by a top-down approach mainly based on electron beam lithography and reactive ion etching (see Fig 1) [3]. The nanowire surfaces have been appropriately functionalised for the respective analytes of interest. A series of experiments (see Fig. 2) for sensing the ionic strength (see Fig. 3) and the pH value of buffer solutions have proven the excellent sensitivity of the fabricated sensors [3,4]. Moreover, sensing of the protein streptavidin at a concentration as low as 580 zM has been observed (see Fig. 4), which is by far the lowest concentration of this protein ever detected and corresponds to detection in the range of only few molecules.

To explain the ultrahigh sensitivity of JNT sensors, we will discuss in detail two advantages of JNTs over the classical MOSFETs [1-4], which are especially important for their application as sensors:

1. The current flow in JNTs is not controlled by a reverse biased p-n junction as in standard MOSFETs but entirely by the gate potential modulating the carrier density in the channel. Thus they are more sensitive to any change in the electrostatic potential on the channel surface acting as a gate potential.

2. JNTs demonstrate bulk conductance near the centre of the channel, in contrast to the conductance in a thin surface inversion or accumulation layer near the gate in the classical inversion mode or accumulation mode transistors, which leads to higher drive currents. Moreover, this fact makes the modulation of depletion and the conduction in JNTs less affected by the noise-inducing parasitic surface states than in the case of conventional MOSFETs, which is very important for achieving high signal-to-noise ratio and hence low detection limit [6,7].

The ultrahigh sensitivity of JNT sensors, combined with their very simple structure and relaxed fabrication process, makes them promising candidates for cheap mass production by the conventional microelectronic technology. This can enable their numerous applications in various fields where fast, low-cost, label-free, low-volume and real-time detection of chemical and biological species at low detection levels is required.

[1] J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nature Nanotech. 5 (2010) 225-229.
[2] J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Solid State Electron. 65-66 (2011) 33-37.
[3] Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Microelectron. Eng. 118 (2014) 47-53.
[4] Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, in A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre, eds., Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting, (Springer International Publishing AG, Cham, Switzerland, Ch. 17, 2014) 367-388.
[5] Y. M. Georgiev, N. Petkov, R. Yu, A. M. Nightingale, E. Buitrago, O. Lotty, J. De Mello, A. M. Ionescu, J. D. Holmes, Nanotechnology (2019), accepted, https://doi.org/10.1088/1361-6528/ab192c
[6] N. K. Rajan, D. Routenberg, M. Reed. Appl. Phys. Lett. 98 (2011) 264107.
[7] K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. L. Stoop, S. Rigante, J. Brunner, W. Fu, C. David, M. Calame, J. Gobrecht, C. Schönenberger. Sensor. Actuat. B-Chem. 191 (2014) 270.

The paper reports on implantation damage accumulation, Ag distribution and the interior morphology in different crystallographic orientations of implanted samples of cubic yttria-stabilised zirconia (YSZ). (100)-, (110)- and (111)-oriented YSZ was implanted with 400-keV Ag⁺ ions at ion fluences from 5 × 10¹⁴ to 5 × 10¹⁶ cm⁻². Rutherford backscattering spectrometry (RBS) in the channelling mode (RBS-C), as well as X-ray diffraction (XRD), were used for the quantitative measurement of the lattice disorder and Ag distribution. The defect propagation and Ag accumulation were observed using transmission electron microscopy (TEM) with the energy-dispersive X-ray spectroscopy (EDX). Although similar damage evolution trends were observed along with all channelling directions, the disorder accumulation is lower along the <110> direction than along the <100> and <111> direction. The damage extends much deeper than the theoretically predicted depths. It is attributed to long-range defect migration effects, confirmed by TEM. At the ion fluence of 5 × 10¹⁶ cm⁻², nanometre-sized Ag precipitates were identified in the depth of 30–130 nm based on the Ag concentration–depth profiles determined by RBS.

Group IV semiconductor nanowires (NWs) are very attractive because of the variety of possible applications as well as of the good silicon (Si) compatibility, which is important for their integration into the existing semiconductor technology.

We will give an overview of our activities on fabrication and application of group IV NWs. These include top-down fabrication (based on electron beam lithography and reactive ion etching) of Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up (vapour-liquid-solid, VLS) growth of alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1 and diameters of 50-70 nm. We will also discuss the innovative nanoelectronic devices that we are working on: junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we will present results on Si JNTs for sensing application as well as on Ge and GeSn JNTs for digital logic. We will also show results on Si RFETs as well as preliminary data on SiGe and GeSn RFETs, which are expected to outperform the Si RFETs.

During the last 1-2 decades semiconductor nanowires (NWs) have received significant academic and commercial attention due to their attractive electrical and mechanical properties and large surface area to volume ratios. They have a variety of possible applications including nanoelectronics, nanophotonics, photovoltaics, sensorics, etc. Among all semiconductor NWs the ones based on group IV materials have the advantage of being the most silicon (Si) compatible. This is very important since their integration into the existing semiconductor technology platform can be relatively easy.

We will give a general overview of our activities on group IV nanowires. We will first present the NWs that we are working with, including top-down fabricated Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up grown alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1, diameters of 50-70 nm and lengths of 1 to 3 µm. We are currently working also on the fabrication of alloyed SiGe and SiGeSn NWs with varying content of the different materials.

Next, we will discuss the innovative nanoelectronic devices that we are working on, namely junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we are fabricating Si JNTs for sensing application as well as Ge and GeSn JNTs for digital logic. Concerning RFETs, we are currently working on Si RFETs and commencing activities on SiGe and GeSn RFETs, which are expected to outperform the Si RFETs.

Finally, we will briefly present a novel device concept that we recently invented: a specific group IV heterostructure band-to-band tunnel FET (TFET). The fabrication process of this device is scalable and fully CMOS compatible and should allow the achievement of high on-current Ion together with low off-current Ioff, hence steep subthreshold slope.

Charge exchange and kinetic energy loss of slow highly charged xenon ions transmitted through freestanding monolayer MoS₂ are studied. Two distinct exit charge state distributions, characterized by low and high charge exchange, are observed. They are accompanied by smaller and larger kinetic energy losses, respectively. High charge exchange is attributed to two-center neutralization processes, which take place in close impact collisions with the target atoms. Experimental findings are compared to graphene as a target material and simulations based on a time-dependent scattering potential model. Independently of the target material, experimentally observed charge exchange can be modeled by the same electron capture and de-excitation rates for MoS₂ and graphene. A common dependence of the kinetic energy loss on the charge exchange for MoS₂ as well as graphene is also observed, which additionally underlines the common nature of the two-center Auger neutralization process. Considering the similarities of the zero band gap material graphene and the 1.9 eV direct band gap material MoS₂, we suggest that electron transport on the femtosecond time scale is dominated by the strong influence of the ion’s Coulomb potential in contrast to the dispersion
defined by the material’s band structure.

Meniscus velocity in continuous casting process is critical in determining the quality of the steel. Due to the complex nature of the various interacting phenomena in the process, designing model-based controllers can prove to be a challenge. In this paper a NARX neural network model is trained to describe the complex relationship between the applied magnetic field from an Electromagnetic Brake (EMBr) and the meniscus velocity. The data for the model is obtained using a laboratory scale continuous casting plant. The next step was to use Adaptive Model Predictive Control (MPC) to deal with the non-linearity of the model by adapting the prediction model to the different operating conditions. The controller will utilize the EMBr as an actuator to keep the meniscus velocity within the optimum range, and reject disturbances that occur during the casting process such as changing the casting speed.

The flow pattern in the mould of the continuous casting is an important factor in determining the quality of the steel slabs that are produced in the end of the process. Hence it can heavily influence manufacturing costs due to the scrap percentage. Electromagnetic actuators are frequently used in the continuous casting process to stabilize the flow in the mould and therefore produce higher quality of steel slabs. Usually they are used in open loop but their effect on the flow pattern may be much better directed if they are used as a part of closed loop control based on real time measurements. In this paper, a closed loop controller is proposed that adjusts the magnetic field of an electromagnetic brake using the real time measurement of the angle of the jet flowing from the Submerged Entry Nozzle (SEN). The angle is kept within a specific range by the controller in order to prevent a deeper jet impingement into the mould; this allows us to achieve the desirable double roll flow pattern, and to avoid the entrapment of slugs. The controller is based on a model of the relationship between brake current and jet angle that was obtained using experimental data from a laboratory scale continuous casting plant.

Nozzle clogging contributes heavily to quality issues seen during the process of continuous casting. The presence of clogging in the Submerged Entry Nozzle (SEN) can significantly change the flow patterns in the mould and therefore impact the quality of the steel product. Also, there is a high risk of inclusions due to parts of the clogging material breaking off and entering the mould. In this paper, we propose a new sensor setup that allows us to detect clogging in the SEN by monitoring the angle of the exiting jet. Based on this clog detection setup, a switched MPC controller is used to keep the angle of the exiting jet between the optimum ranges using an Electromagnetic Brake. This allows the controller to keep the angle of the jet in the optimum range even when clogging occurs in the nozzle. Experimental data from a laboratory scale continuous caster is used to derive the models for the controller.

The Institute of Resource Ecology / Helmholtz-Zentrum Dresden-Rossendorf is operating the Rossendorf Beamline (ROBL/BM20) at the European Synchrotron Radiation Facility (ESRF) for 20 years. We are constructing a second experimental hutch with two new diffractometers for single crystal, powder and surface diffraction. The single crystal diffractometer is foreseen for small and large molecule crystallography, mainly for structures with heavy metals. This diffractometer is equipped with a Pilatus3 X 2M detector mounted in a sturdy metal frame on a granite table. Sample-detector distances can be varied between 140 und 600mm. Three goniometers are available to mount single crystals: a Huber Kappa goniometer 512.410, an Arinax Kappa MK3, and a Huber uniaxial goniometer 410. The energy range of 5-35keV allows the application of anomalous dispersion. In-situ experiments on single crystals and powders are supported. Diffraction measurements can be combined simultaneously with XANES and XRF spectroscopy using a Vortex X90 CUBE silicon drift detector with a FalconX1 processor.
The second diffractometer will be used for surface diffraction and moderate high-resolution powder diffraction. This diffractometer is a 6-circle Huber diffractometer with Eulerian cradle geometry. Surface and powder diffraction techniques comprise specific setups. Both techniques will use a Pilatus 100k detector. The resolution for powder diffraction using the Pilatus 100k detector does not reach the resolution of synchrotron diffractometers with secondary analyzer crystals, but provides a magnitude better resolution than lab diffractometers. A specific support allows the installation of the Vortex X90 detector also on this diffractometer. The setup comprises a cryo cooler (80-400 K) and a heater (up to 1200 K) which can be installed at both diffractometers. The experimental hutch is equipped for the use of radioactive material.

The control of the liquid steel flow in the mould of a continuous caster based on real time flow measurements is a challenging task due to the lack of appropriate measurement techniques. The opaqueness, the high temperature of 1500 C and the chemical aggressiveness of the melt require non-optical contactless methods. In order to reconstruct the complex flow structure in the mould, the Contactless Inductive Flow Tomography (CIFT) is a promising candidate, since it allows the visualization of the flow structure in the melt by applying a magnetic field to the melt, measuring the flow induced perturbation of that field and solving subsequently a linear inverse problem. The combination of this new measurement technique with typical electromagnetic actuators like electromagnetic brakes used in continuous casting, pose a challenge to the CIFT measurement system, because the flow induced magnetic field is in the range of 100 nT and has to be measured robustly on the background of the static magnetic field with the amplitude of 300 mT generated by the brake. In this work we will show recent developments regarding this topic for a small model of a continuous caster in the lab.
Furthermore, we will present a new method on how the complex linear inverse problem can be solved in real time providing a time resolution of about 1 Hz.

Solid state welding technologies enable dissimilar metal welding without critical intermetallic phase formation. Magnetic Pulse Welding (MPW) is a promising joining method for hybrid sheet connections in car body production or for manufacturing of dissimilar tube connections. Given a suitable MPW process design, the shear testing of MPW joints usually leads to failure in the weaker base material. This finding emphasizes the high strength level of the joining zone itself. Consequently, the transmission of higher forces or torques, respectively, requires stronger materials or adapted geometries. In the present experimental study, the diameter of an exemplary driveshaft was doubled to 80 mm at constant tube wall thickness to increase the load bearing capability. The characteristic impact flash was recorded at different positions around the tube’s circumference and it was used to adjust the most relevant process parameters, i.e. working length and acceleration gap, at the lower process boundary. In metallographic analysis, the final shapes of both joining partners were compared with the original driveshaft dummies on macroscopic and microscopic scale. The typical wavy interface between aluminum and steel was analyzed in detail. Doubling the tube diameter lead to four times higher torque levels of failure during quasistatic and cyclic torsion tests.

The geomagnetic field is induced by liquid metal ow inside Earths outer core as a self-excited dynamo. Buoyancy drives the liquid metal flow because the iron rich core is cooling from its primordial state through heat loss to the mantle. The rotation of the Earth and Lorentz forces alter the resulting convective flow. However, since a 3000 km thick rocky mantle hinders our ability to observe core dynamics, the detailed ow topology is still largely unknown. Here we will investigate the effect of rotation on a low Prandtl number thermal convection by means of laboratory experiments and DNS. Therefore, we consider a rotating Rayleigh-Bénard convection setup in an upright cylindrical vessel of aspect ratio Γ = D/H = 2. We investigate supercriticalities in the range of 1 < R < 20 and Ekman numbers 4x10^-4 < Ek < 5 x 10^-6 in liquid gallium at Pr = 0.03. We find that oscillatory convection generates velocity that appear to exceed predictions in steady convection. Multi-modal bulk oscillations dominate the vertical velocity field over the whole range of supercriticalities investigated. Additionally, coherent mean zonal flows and time-mean helicity is found in the rotating liquid metal convection. Thus, we show that these oscillatory flows can be relevant for dynamo action.

Fragestellung:

Medulloblastome (MBs) sind die häufigsten malignen Hirntumore im Kindesalter. Die derzeitige Therapie besteht aus Tumorresektion und Radio-Chemotherapie. Dennoch zeigen insbesondere Patienten mit SHH/p53-mutierten- sowie Gruppe-3-MBs eine schlechte Prognose mit einer 5-Jahres-Überlebensrate von nur 41 % sowie 45 %. Verbesserte Therapiestrategien stehen daher im Fokus der aktuellen Forschung.
Unser Projekt kombiniert Radiotherapie (RT) mit dem DNA-de-novo-Methyltransferase-Inhibitor Decitabin (5 Aza 2’-desoxycytidin) und dem Telomerase-Inhibitor Abacavir in einem orthotopischen MB Mausmodell, da in 70 % der primären MBs eine aberrante Hypermethylierung beziehungsweise erhöhte Telomeraseaktivitäten nachgewiesen wurden. Zudem konnten wir in vitro bereits zeigen, dass die Kombinationsbehandlung mit RT, Decitabin und Abacavir das klonogene Überleben signifikant verringert.
Methodik:
Alle Tierexperimente wurden durch die Landesdirektion Sachsen genehmigt (Reg.-Nr: TVV 30/14). NSG-Mäusen wurden Gruppe-3-MB-PDX-Zellen (DKFZ Heidelberg, Dr. Kool) stereotaktisch ins Cerebellum injiziert. Drei Wochen postoperativ wurde den Tieren täglich über 14 Tage Decitabin (0,1 mg/kg/Tag) und/oder Abacavir (50 mg/kg/Tag) intraperitoneal verabreicht. Die lokale Einzeit-Bestrahlung (2 Gy) erfolgte am Tag 8. Mit Erreichen der definierten Abbruchkriterien wurden die Mäuse euthanasiert (= Überlebenszeit) und die Gehirne kryokonserviert. Im Anschluss wurden Gefrierschnitte immunhistologisch angefärbt und die mittlere Anzahl proliferierender Zellen (Ki-67) sowie die Vaskularisierung (CD31) im Tumor ermittelt.
Die statistische Auswertung erfolgte mit n = 10 Tieren je Behandlungsgruppe mittels Mann-Whitney-Test (medianes Überleben) bzw. zweiseitigem T-Test (Ki-67; CD31) zur unbehandelten Kontrollgruppe.
Ergebnis:
Zum Behandlungsstart war eine Tumorgröße von 1 mm nicht überschritten, was durch wöchentliche MRT-Untersuchungen (1-Tesla-Kleintier-MRT/PET Gerät Mediso) nachgewiesen wurde. Die Überlebensanalyse zeigte eine signifikante Verlängerung des medianen Überlebens nach multimodaler Behandlung (RT, Decitabin, Abacavir; 66 ± 9 Tage) vs. der unbehandelten Kontrollgruppe (44 ± 2 Tage) und Bestrahlung (50 ± 1 Tage). Sowohl die Behandlung mit RT+Decitabin (55 ± 3 Tage), als auch mit RT+Abacavir (59 ± 6 Tage), zeigte eine signifikante Überlebenszeitverlängerung vs. Kontrolle, aber nicht vs. RT. Die Proliferation und die Vaskularisierung waren in den multimodal behandelten gegenüber den Kontrolltumoren signifikant (p ≤ 0,05) um 15 % bzw. 14 % verringert.
Schlussfolgerung:
Die multimodale Therapie mit Radiotherapie, Decitabin und Abacavir konnte das Überleben von Mäusen mit orthotopischem Gruppe-3-Medulloblastom signifikant verlängern. Die Therapie zeigt damit klinisch relevantes Potential, welches wir derzeit im Shh/p53-mutierten MB-Mausmodell evaluieren.
Fördermittel:
Das Projekt wird durch die Else Kröner-Fresenius-Stiftung (2016_A184) und die Janssen-Cilag GmbH (DEC-I-17-DEU-001-V01) unterstützt.

The effects of current induced Néel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn₂Au thin films were investigated by x-ray magnetic linear dichroism–photoemission electron microscopy. We observed current induced switching of antiferromagnetic domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible Néel vector reorientation was obtained in different parts of the samples and the switching of up to 30% of all domains in the field of view of 10 μm is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attributed to current induced Néel vector switching in Mn₂Au.

Cubic crystal structure and regular octahedral environment of Ir⁴⁺ render antifluorite-type K₂IrCl₆ a model fcc antiferromagnet with a combination of Heisenberg and Kitaev exchange interactions. High-resolution synchrotron powder diffraction confirms cubic symmetry down to at least 20 K, with a low-energy rotary mode gradually suppressed upon cooling. Using thermodynamic and transport measurements, we estimate the activation energy of Δ ≃ 0.7 eV for charge transport, the antiferromagnetic Curie-Weiss temperature of θ_CW ≃ −43 K, and the extrapolated saturation field of H_s ≃ 87 T. All these parameters are well reproduced ab initio using U_eff = 2.2 eV as the effective Coulomb repulsion parameter. The antiferromagnetic Kitaev exchange term of K ≃ 5 K is about one half of the Heisenberg term J ≃ 13 K. While this combination removes a large part of the classical ground-state degeneracy, the selection of the unique magnetic ground state additionally requires a weak second-neighbor exchange coupling J₂ ≃ 0.2 K. Our results suggest that K₂IrCl₆ may offer the best possible cubic conditions for Ir⁴⁺ and demonstrates the interplay of geometrical and exchange frustration in a high-symmetry setting.

We have studied electron spin resonance (ESR) absorption spectra for the nonmagnetically diluted strongleg spin ladder magnet (C₇H₁₀N)₂Cu_(1−x)Zn_xBr₄ (abbreviated as DIMPY) down to 450 mK. Formation of the clusters with nonzero net magnetization is confirmed; the cluster-cluster interaction is evidenced by the concentration dependence of ESR absorption. High-temperature spin-relaxation time was found to increase with nonmagnetic dilution. The ESR linewidth analysis proves that the Dzyaloshinskii-Moriya (DM) interaction remains the dominant spin-relaxation channel in diluted DIMPY. Experimental data indicate that the Dilution results in the weakening of the effective DM interaction, which can be interpreted as total suppression of DM interaction in the close vicinity of impurity atom.

We report on an experimental investigation of adiabatic bubbly two-phase flow development in a DN50 pipe with a ring-shaped and a baffle-shaped constriction at different superficial velocities of gas (up to jg = 0.1400 m·s-1) and liquid (up to jl = 1.6110 m·s-1) using ultrafast electron beam X-ray computed tomography (UFXCT). From UFXCT images, cross-sectional gas holdup distributions were obtained with a temporal resolution of up to 2,500 frames per second in 18 scanning planes along the pipe. A sophisticated data processing approach was applied to extract gas holdup data immediately from the two-phase flow image stack. Based on that, time-averaged gas holdup of the cross-section and the axial center of the pipe were calculated. In addition, bubble sizes and velocities were determined.

The municipal wastewater collection system is recognized as an initial point of interaction between microplastics (MPs) and the urban wastewater matrix. The raw wastewater contains a wide variety of organic and inorganic substances including chemicals and heavy metals. However, the fate of MPs in urban sewer systems is not yet well understood. In this work two types of virgin polypropylene (PP) samples, isotactic (iPP) and atactic (aPP), were exposed to two synthetic wastewater solutions in order to study their effects on the physical properties of the hydrophobic polymer surfaces. Particular attention was paid to the pollution adhesion at the air-liquid-solid interfaces of the surface air pockets entrapped on the polymer surfaces. The first wastewater solution consists of mixed fat, oil and grease (FOG) - surfactant and another which is an exclusively contained wastewater surfactant. The interaction experiment over a period of 10 min between the polymer’s air pocket and solutions indicated that the size of the bubble in the mixed FOG-surfactant solution increased more pronouncedly for iPP (%152) in contrast to aPP (%31) and was also compared with the greater surface roughness of the polymers. The size variation of the spherical cap on the immersed polymer surfaces were measured between 17 µm and 85 µm using image processing techniques while the data was analyzed by the Young-Laplace equation. The corresponding technical surface roughness of the polymers, the surface tension of the liquids and their air/water contact angle on the flat polymer surfaces were also measured. The results of this study indicated that surface air pockets influence the adsorption capacity of MPs and thus their buoyancy and contamination potential.

Short period superlattices (SPSs) of InxGa1-xN/GaN quantum wells (QW) with a thickness of one up to just a few atomic monolayers (MLs) are promising for bandgap and strain engineering towards advanced optoelectronics devices and novel topological insulators.

We have considered 5-period InxGa1-xN/GaN SPSs deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates under metal-rich conditions. The nominal QW thickness was 1 ML and the GaN barriers were 10 nm thick. The SPSs were grown at various growth temperatures keeping the same temperature for both QWs and GaN barriers.

Cs-corrected high resolution transmission electron microscopy (HRTEM), and probe-corrected scanning TEM (HRSTEM) observations were carried out in order to elucidate the effect of growth temperature on the structural quality, composition, and strain state of the QWs. Cross-sectional observations were conducted along the <11-20> and <1-100> projection directions. Atomic positions were identified on images using a peak finding algorithm and were employed in order to extract nanoscale strain maps. Furthermore, quantification of the Z-contrast of atomic columns on the HRSTEM observations was employed for the direct determination of the indium content in QWs. The thin foil relaxation phenomenon was considered in the analysis.

Composition dependent strain graphs were calculated theoretically in order to associate the experimental strain measurements to the indium content. For that purpose, a series of energetically relaxed InxGa1-xN/GaN supercells were constructed taking into account several indium contents, and the QW thickness limited to 1 ML. For the relaxation of the supercells a ternary empirical interatomic potential was utilized using molecular dynamics simulations.

The helium ion microscope (HIM), well known for its highresolution
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.; Nanometer scale
elemental analysis in the helium ion microscope using time
of flight spectrometry, Ultramicroscopy 162(2016): 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von
Borany, J.; Time-of-flight secondary ion mass spectrometry
in the helium ion microscope, Ultramicroscopy 198(2019),
10-17

Introduction/Purpose: Short period superlattices (SPSs) comprising ultrathin InGaN/GaN quantum wells (QW) with thicknesses ranging from one to few (0002) monolayers (MLs) are promising for novel applications ranging from band gap engineering in optoelectronic devices to topological insulators. The strain relaxation behavior of a range of samples grown by varying the growth temperatures for the QWs and GaN barriers has been considered.
Methods: In(Ga)N/GaN SPSs were deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates. Structural characterization was performed by high resolution transmission and scanning transmission electron microscopy (HRTEM/HRSTEM).
Results: Strain relaxation through formation of stacking fault domains was observed with decreasing growth temperature. For the quantification of strain versus composition, peak finding with a recently established approach was implemented. This involves quantification of Z-contrast from HRSTEM observations by comparison with calculated composition-dependent graphs of InxGa1-xN/GaN atomic column intensity ratios obtained from multislice image simulations of energetically relaxed supercells under the frozen lattice approximation. Energetical relaxation was performed by molecular dynamics using an empirical interatomic potential, considering the ordered, disordered, and island models of QW structure. Comparison to the experimental observations was performed along the a-type zone axis that is appropriate to deduce average values for the QW composition and strain.
Conclusions: The investigation concluded to the influence of growth temperature in the composition and structural properties of ultra-thin In(Ga)N/GaN QWs.

The European H2020 project “ion4SET” is directed to the development of advanced computation and communication devices with significantly lower power consumption. The general objective is to demonstrate the manufacturability of single electron transistors (SETs) using CMOS compatible technology. The basic idea of this SET is a nano-pillar (NP) transistor having a single Si nanodot (ND) in the oxide layer separating source and drain. The ND is formed by ion beam mixing and post annealing from a Si top layer. The ion irradiation under normal incidence is a crucial process for the small nano-pillars which are only 10 to 30 nm in width and about 80 nm in height.
In this work the evolution nano-pillars shape is investigated under heavy ion irradiation from a mass separated focused ion beam (FIB) for different ion energies at RT and 400°C target temperature. In particular Si (60 keV), Pb (30 and 60 keV), Au (30 and 60 keV) ions as well as polyatomic projectiles Au2 and Au3 (Uacc = 30 kV) with a fluence of 5 x 1015 cm-2 were applied.
Whereas the Si ion irradiation of Si pillars at elevated temperatures only deforms the pillar tip, the heavy ion irradiation leads depending on the fluence up to a total removing of the pillar. The fluence variation was obtained on the slope of the beam profile. The irradiation at RT with Pb ions at 30 keV showed a more pronounced bending of the pillar due to the high energy deposition caused stress and viscous flow than that at 60 keV. The influence of the irradiation is also depending on the thickness and the distance of the pillars in different lithographic prepared fields. For a better comprehension of the irradiation results the experiments were simulated using the TRI3DYN code.

Transmission imaging with helium ions is expected to offer contrast not possible with electron beams. Whilst MeV helium ion transmission imaging is possible1, sub-50 keV helium ions are more widely available, for example, in helium ion microscope (HIM) machines. These HIM systems can perform high-resolution secondary electron imaging as well as secondary ion mass spectrometry (SIMS) elemental analysis2. Despite recent interest in the transmission imaging capabilities of low energy helium3, this method still requires detailed evaluation. Time of flight (TOF) spectroscopy for backscattered helium in a HIM has also been reported4 but transmission TOF energy spectroscopy with sub-50 keV energy helium remains unexplored. This technique should obtain information not accessible using solely transmission images.
This work focuses on the contrasts available using sub-50 keV He+ in a transmission-HIM (THIM). Our experiments used an in-house developed THIM utilising a duoplasmatron ion source operated below 50 kV. Powdered crystals of BN, NaCl and MgO were investigated in the THIM, using 10 keV He+ stationary beam illumination. A large scattering effect was visible (fig. 1B) and has been explained by sample charging, which will require consideration in all future THIM imaging experiments. Scanning THIM (STHIM) results will also be discussed, SE and STHIM images were recorded in parallel for a Cu mesh (fig. 1C ). As an additional mode, deflector plates can pulse the primary beam, allowing our THIM to record STHIM-TOF spectra (see fig. 1D) .We will also present selected recent results obtained using our in-house developed SIMS system, attached to a Zeiss Nanofab HIM2. Fig. 2 shows images from a CIGS photovoltaic solar cell active layer, containing Na, In and Cu. HIM-SIMS can efficiently analyse the nanometre scale distribution of Na, the presence of which can reduce the efficiency of the solar cell.
Funding from Luxembourg National Research Fund (FNR) project STHIM (C16/MS/11354626) and EU Horizon 2020 Grant No. 720964.

Figure 1 A) THIM image of MgO sample on Cu grid, hole width 108 µm bar width 19 µm (scale bar approx. 2.5 mrad), B) a spot pattern from MgO. C) SE and STHIM images of a Cu grid recorded in parallel, hole width approx. 90 µm. D) TOF spectrum of source emission for 10 keV He+.

Figure 2A) HIM-SE image and HIM-SIMS images showing the distributions of Na, In and Cu for an active layer of a CIGS solar cell. SE image recorded using 20 keV He+, SIMS images recorded, using 20 keV Ne+ ions, in a Zeiss Nanofab equipped with an in-house developed SIMS system. Field of view is 10 µm.

1. Watt, F. et al. Whole cell structural imaging at 20 nanometre resolutions using MeV ions. Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6–11 (2013).
2. Dowsett, D. & Wirtz, T. Co-Registered In Situ Secondary Electron and Mass Spectral Imaging on the Helium Ion Microscope Demonstrated Using Lithium Titanate and Magnesium Oxide Nanoparticles. Anal. Chem. 89, 8957–8965 (2017).
3. Wang, J. et al. Focussed helium ion channeling through Si nanomembranes. J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 36, 021203 (2018).
4. Klingner, N. et al. Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry. Ultramicroscopy 162, 91–97 (2016).

III-As semiconductors in the form of free-standing nanowires have exhibited new potentials for a wide variety of future applications in nanotechnology, ranging from energy-efficient electronic switches to entangled-photon-pair sources for quantum information technology, including the possibility for monolithic integration in the mainstream Si technology. Using molecular beam epitaxy, we developed an in situ procedure (substrate annealing – Ga deposition – substrate annealing) in order to modify the surface of Si substrates and, thus, to achieve highly synchronized nucleation of self-catalyzed GaAs nanowire ensembles with well controlled dimensions and number density. Specifically, the radius can be as low as 10 nm, the distribution of lengths can be sub-Poissonian (due to the so-called nucleation anti-bunching), and the number density can be varied from 10 ⁶ to 10 ⁹ cm-2.
Furthermore, the GaAs nanowires can be hydrostatically strained when they are overgrown all-around with lattice-mismatched shells. The high surface-to-volume ratios allow for growing highly mismatched combinations without dislocations, beyond to what is possible in thin-film heterostructures. Here, we show that the mismatch strain inside the GaAs core can be engineered via the composition and the thickness of an (In, Ga)As or (In, Al)As shell. As a result, the electronic properties of GaAs can be widely tuned; the band gap and the electron effective mass can be reduced down to 60% of the strain-free values, rendering GaAs nanowires suitable for photonic devices across the near-infrared (800 – 1400 nm) range or for high-speed transistors.

Free-standing nanowires are promising platforms for hosting three-dimensional heterostructures such as single quantum dots for quantum photonics, modulation doped heterostructures for gate-all-around high mobility transistors, etc. The peculiarity of heteroepitaxy in nanowires is the existence of multiple growth interfaces with different crystallographic orientations (usually one top- and six side-facets), where the growth can take place in different modes (e.g. vapor-liquid-solid on the top- and vapor-solid on the side-facets) and can be controlled independently. Furthermore, strained epilayers in nanowires can relax elastically both at the lateral free surface and by stretching the substrate, which in this case are the thin nanowires. All these features open up new possibilities for complex three-dimensional heterostructures with loose strain restrictions.
Here, we have investigated the growth of radial and axial heterostructures, as well as combinations of the two, within III-As nanowires. The radial ones consist of thin GaAs nanowires overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. In agreement with theory, the small volume of the core allows for strain engineering both in the core and the shell, and for realization of highly-mismatched/strained heterostructures (with misfits up to 4%) without dislocations. The manipulation of the growth kinetics is necessary in order to suppress strain-driven phenomena, such as the preferential shell-growth and In-incorporation on one side of the core. The axial heterostructures consist of single or multiple GaAs/AlxGa1-xAs quantum dots. The width and the thickness of these dots can be controlled independently. The AlxGa1-xAs segments were grown as digital alloys using pulsed epitaxy in order to achieve sharper interfaces and to avoid the formation of stacking faults. Finally, we realized complex heterostructures with single GaAs/AlxGa1-xAs quantum dots inside the core of core/shell nanowires, aiming at engineering the electronic properties of the dots depending on the composition and thickness of the shell.
Besides MBE experiments, our investigations involved transmission electron microscopy (HR-TEM, STEM, EDX, STEM tomography), X-ray diffraction, Raman scattering spectroscopy, and photoluminescence spectroscopy.

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.

Single quantum dots in the core of freestanding semiconductor nanowires is a promising scheme for the realization of on-demand sources of single photons or entangled photon pairs in quantum technology systems. Here, we demonstrate that complex quantum-dots can be grown in self-catalyzed III-As nanowires and their emission can be tuned in a wide range of wavelengths.
The quantum dots are formed inside self-catalyzed GaAs nanowires (grown on Si substrates by molecular beam epitaxy) by first growing an axial AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructure in pulsed mode . The AlxGa1-xAs segments are grown as digital alloys with a precise control of the composition, the thickness, and the crystal structure (absence of stacking faults). Then, the nanowires are overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. Owing to the large lattice-mismatch with the shell, the thin core develops tensile hydrostatic strain and the emission from the dot is strongly red-shifted. Furthermore, distinct exciton-biexciton features are identified in photoluminescence measurements.

The recent availability of high-brightness helium ion sources has enabled exciting new possibilities in the fields of microscopy and nanofabrication. When compared to electron beams of same energy, He+ ions have a smaller interaction volume and thus offer higher lateral resolution (< 0.5 nm) in the secondary electron (SE) imaging mode1. While the majority of the applications of the commercial Helium Ion Microscope - HIM (Zeiss Nanofab) have been in SE imaging and nanofabrication, the complete range of imaging possibilities is still not fully explored. In this context, transmission ion microscopy is expected to offer new contrast mechanisms (e.g. charge neutralization) which are not possible in a Transmission Electron Microscope (TEM). Transmission microscopy using MeV He+ ions has already been demonstrated2, but, they are not very widely available. With the increasing availability of HIM which operate at primary energies below 50 keV, the potential to use it for transmission ion microscopy and ion energy-loss spectroscopy still need to be fully explored. To address this, we developed a prototype Transmission Helium Ion Microscope (THIM) that can operate on both stationary full-field THIM mode as well as Scanning THIM (STHIM) mode with simultaneous SE imaging possibility. This prototype has a duoplasmatron ion source and offers full flexibility in terms of instrumental configurations. This is a significant advantage in comparison to using the commercial instrument in which space below the specimen plane is very limited and thus restrict the possible experimental configurations. We imaged BN, NaCl and MgO crystalline powders in the stationary full-field THIM imaging using 10 keV He+ and investigated the distribution of transmitted ion intensities. The scattered intensity form unexpected spot patterns that may be explained by sample charging and morphology. Furthermore, we have added electronics to pulse the primary ion beam in the prototype instrument. This allows us to perform Time-of-Flight (TOF) multispectral imaging in both THIM and STHIM modes in addition to the standard Bright-Field, Dark-Field and SE imaging modes. Our presentation will focus mainly on the transmission ion configuration. We will also briefly discuss the recent developments in the Secondary Ion Mass Spectrometers (SIMS) that we developed for Zeiss Nanofab instruments (HIM-SIMS) which allow direct chemical mapping at nanoscale.
1 G. Hlawacek and A. Gölzhäuser, editors , Helium Ion Microscopy, 1st ed. (Springer, 2016).
2 F. Watt et al, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6 (2013).

The Helium Ion Microscopes (HIM) provides spot sizes up to 0.5 nm for Helium and 1.8 nm for Neon ion beams. 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.

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]. It is based on fast blanking electronics that chop the primary beam into pulses with a minimal length of 20 ns. An ion optic has been designed and optimized for high extraction and transmission efficiency of sputtered secondary ions. The high transmission is crucial to collect enough signal from nano-particles prior to their complete removal by ion sputtering. Currently the sample will be tilted towards the extraction optic and will be constantly biased to +/- 500 V to accelerate the ions into the extraction nozzle.

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. The beam resolution has been evaluated to 8 nm using the knife edge method, and unpulsed beam and a 75%/25% criterion. We will show an outlook on adding a delayed secondary ion extraction.

References

[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.; (2019) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, Ultramicroscopy 198, 10-17

The development of high voltage Li-ion battery materials has been hindered by undesired reactions at the electrolyte-electrode interface. Here, the process of cathode electrolyte interphase (CEI) formation in high voltage cathode material, LiCoPO4, has been investigated for the first time using Helium Ion Microscopy (HIM), and in-situ Time-of-Flight (ToF) Secondary Ion Mass Spectrometry (SIMS). The combination of HIM and Ne-ion ToF-SIMS has been used to correlate the morphology and chemistry of the CEI layer on LiCoPO4 with local cathode microstructure. Helium ion microscopy was found to be capable of imaging the CEI layer with higher resolution than scanning electron microscopy (SEM), and at large fields of view. The CEI layer was found to grow on LiCoPO4 when the cathode was charged, and undergo partial dissolution on discharge. CEI layer coverage on LiCoPO4 was inhomogenous, and typically thinner on larger agglomerates. Ne-ion SIMS characterisation identified the presence of oxyfluorophosphates from HF attack by the electrolyte, and the presence of uncycled Li and potential Co dissolution on the surface. The variable thickness of the CEI layer with inactive Li on the surface of the LiCoPO4 electrodes led to severe degradation over the course of 10 cycles.

Energy cascades, coherent structures, and the arrow of time in turbulence

Energy cascades, coherent structures, and the arrow of time in turbulence

The effects of a vertical constant magnetic field on the flow structure and global transport properties of momentum and heat in liquid metal Rayleigh-Bénard convection are investigated. Experiments are conducted in a cylindrical convection cell of unity aspect ratio, filled with the alloy GaInSn at a low Prandtl number of Pr = 0.029. Changes of the large-scale velocity field structure with increasing magnetic field strength are probed using multiple ultrasound Doppler velocimetry sensors and thermocouples for a Rayleigh number range of 10^6 < Ra < 6x10^7 and Hartmann numbers Ha < 1000. Our simultaneous multi-probe temperature and velocity measurements demonstrate how the large-scale circulation is affected by an increasing magnetic field strength (or Hartmann number). Lorentz forces induced in the liquid metal first suppress the oscillations of the large-scale circulation, then transform the one-roll structure into a cellular large-scale pattern consisting of multiple up- and downwellings, before finally expelling any fluid motion out of the bulk leaving only a near-wall convective flow that persists even below Chandrasekhar's linear instability threshold. Our study thus proofs experimentally the existence of wall modes in confined magnetoconvection. The magnitude of the transferred heat remains nearly unaffected by the steady decrease of the velocity momentum over a large range of Hartmann numbers. Previous experiments and direct numerical simulations are consistent with our results.

We require a compact magnetic field measurement system that is able to measure alternating magnetic flux densities in the nanotesla range on the background of signals with constant amplitudes of some hundred millitesla. The signal of interest has a frequency of a few Hertz and must be measured with an amplitude error smaller than 0.1% and a phase error no larger than 10⁻¹ deg. For this we present theoretical and experimental analyses of absolute and first order gradiometric induction coil sensors with sensitivities larger than 500 V/T/Hz and diameters of 28 mm. From their equivalent circuits, we derive the associated complex-valued transfer functions and fit these to calibration measurements, thereby determining the value of the equivalent circuit components. This allows us to compensate their non-linear frequency-dependent amplitude and phase behaviour. Furthermore, we demonstrate the optimization of coils based on Brooks' design of equal squares in the adaptation by Murgatroyd, which maximizes the inductance (and thereby most likely the sensitivity) of the coils. Finally, we design a new coil with a diameter of 74 mm and a sensitivity of 577 V/T/Hz with an analytically predicted equivalent magnetic field noise of around 40 pT/√Hz in the 1 Hz frequency range, which is then confirmed by measurements on the manufactured prototype.

We report on laboratory experiments focusing on bubbling phenomena arising from gas injection through a top submerged lance (TSL) in a liquid metal layer. Visualization was performed in the eutectic alloy GaInSn using X-ray radiography. Argon bubbles were injected through the nozzle positioned at three different submergence depths. Essential parameters such as the bubble size, bubble shape, detachment frequency or the two-dimensional gas distribution in the flat vessel were obtained by image processing. The results show that the deep position of the submerged lance causes an asymmetric large-scale circulation inside the fluid vessel. Bubble detachment frequencies were calculated by Fast Fourier Transformation from fluctuations of the image intensity in the vicinity of the nozzle injection point. This frequency does not show strong variations with respect to changes of the gas flow rate and the submergence depth of the nozzle. An increasing gas flow rate results in an increasing two-dimensional projected bubble area and the occurrence of a significant number of small bubbles being trapped by the strong fluid flow in the liquid metal layer.

The present paper focuses on the application of CFD techniques to investigate the Top-Submerged-Lance (TSL) gas injection in liquid metal.
Previous works of the authors have shown that up- and down-scaling procedures based on the modi-fied Froude number have some shortcomings, as this approach does not take into account the interfa-cial and viscous forces. Indeed surface tension and dynamic viscosity of the smelting slags (σ = 0.4-0.5 N/m, μ = 0.2 Pa·s) are higher than the operating fluids that have been used in literature (water, par-affin oil), which have been used to study TSL injection in down-scaled furnaces.. In order to get closer to real systems, the authors study the TSL injection of Argon in a liquid metal.
An experimental campaign was carried out at the Magnetohydrodynamic Department of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where the eutectic alloy GaInSn was used as liquid phase. The alloy is liquid at room temperature, and X-Ray imaging is used to picture the multiphase flow in a qua-si-2D vessel (140x140x12 mm).
The aim of the present work is to demonstrate the applicability of CFD techniques to model multi-phase flows involving liquid metals, and validate the model using the data produced at HZDR. The commercial software ANSYS Fluent® was used together with the Volume of Fluid model to directly resolve the gas-liquid interphase. Some features of the flow, such as the void fraction distribution and bubble detachment frequency are tracked with CFD and compared to the experimental data. The ef-fect on the hydrodynamics of different operating conditions, such as the lance immersion depth is investigated.
The authors are currently extending the work to new geometries and operating conditions, in order to get a broader amount of data, useful for the validation of models and for the further understanding of the TSL injection.

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

In this study we present an investigation on the impact of sparger configuration and fluid properties on the local gas phase dynamics for up to 17% total gas holdup. Experiments in a bubble column with 100 mm inner diameter were conducted with deionized water and NaOH solution of up to cNaOH = 32 mmol·l−1. Ultrafast X-ray computed tomography (UFXCT) was applied to obtain local hydrodynamic parameters, such as gas holdup distribution, bubble sizes and average bubble rise velocities. Radial gas holdup profiles show wall peaking, which is attributed to the uniform bubbly flow regime generated by the needle sparger used in this study. The addition of NaOH leads to similar gas holdup values but significant changes on local bubbly dynamics, such as bubble size distribution and axial gas phase velocity. The Sauter mean diameter was found to decrease with increasing concentration of NaOH, whereby the decrease is larger at higher gas flow rate.

Visible light driven nano/micro swimmers are promising candidates for potential biomedical and environmental applications. However, the previously reported mean squared displacement (MSD) values are low, typically in the range of up to 200 µm2 (when measured over 10 s), even under the favourable UV light illumination.[1,2]
Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The Ag/AgCl-based micromotor can boost the MSD to a remarkable value of 3000 µm2 (over 10 s) in pure H2O, even when activated with blue light (λ = 450-490 nm). Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] Using numerical simulations of the Langevin equations, we gain a fundamental understanding not only the diffusion constants, but also the system-specific interaction parameter between Janus motors and passive beads.
1. Ibele, M., et al., Angew. Chem. Int. Ed. 2009, 48, 3308.
2. Simmchen, J., et al., ChemNanoMat 2017, 3, 65.
3. Wang, X., et al., Small DOI: 10.1002/smll.201803613.
4. Wang, X., et al., Small 2018, 14, 1802537.

Soft robots have been designed and developed to fulfil the demands of better deformability and adaptability to changing environment [1-2]. These soft robots could be made of various stimuli responsive materials that can be actuated by magnetic field [3], light [4], temperature [5], electric fields [6], chemicals [7], pressure [8], etc. In contrast to other actuation mechanisms, magnetic fields are appealing for numerous application scenarios (e.g. environmental, biological, medical), where the benefits stem from their long-range penetration, easy accessibility, and controllability [2]. Very recently, there are already impressive demonstrations of magnetically triggered millimetre- and centimetre- scaled soft robots performing multimodal locomotion [9] and complex 3D actuations [10]. However, their thick and bulky bodies [9-10] challenge themselves to reveal better performances for specific implantations which require more, for instance, high actuation speed, and reversible large-scale actuation amplitude by a rather low magnetic field.

Here, we present an ultrathin (7-100 μm) and lightweight (1.2-2.4 g/cm3) soft robot that can be actuated in a tiny magnetic field of 0.2 mT reaching full actuation amplitude with a reaction time of 10 ms only. By programming the foils into different geometries, these soft robots are readily used for multifunctional nature-mimicking motion with a magnetic coil or a permanent magnet, such as a quick fly gripping and releasing, complex fast human cross-clapping mimicking, etc.

[1] D. Rus et al., Nature 521, 467 (2015)
[2] L. Hines et al., Adv. Mater. 29, 13 (2017)
[3] J. Y. Kim et al., Nature materials 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nature Materials 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today, 10, 30 (2007)
[7] Q. Zhao et al., Nature communications 5 (2014)
[8] SA. Morin et al., Science, 337, 828 (2012)
[9] W. Hu et al., Nature, 554, 81(2018)
[10] Kim. Y, et al., Nature, 558, 274 (2018)

We investigate directional solidification of the melt with solid inclusions by means of neutron radiography (NR). As NR is a non-invasive imaging technique, the results, for the first time, reveal the particle trapping in the solidifying melt at macro scale. It is shown that particle solidification in volume can be achieved when liquid and solid phases form mushy zone. Experiments were performed using a rectangular vessel containing tin which was electromagnetically stirred and directionally solidified. Information about the recirculating flow was gathered by tracing 355-500 μm gadolinium (Gd) particles which visualize the flow field and phase composition in any given time. The findings show that metallurgical challenges, e.g. stirring and homogenously dispersing ceramic reinforcement material in MMC, could be solved by applying electromagnetic treatment while melt is in semi-solidus state.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large thermal hysteresis at their firstorder martensitic phase transition which hinders a technological application in magnetic refrigeration. By optimizing the Cu content in Ni₂Cu_xMn_1.4−xIn_0.6, we obtained a thermal hysteresis of the martensitic phase transition in Ni₂Cu_0.2Mn_1.2In_0.6 of only 6 K. We can explain this very small hysteresis by an almost perfect habit plane at the interface of martensite and austenite phases. Application of hydrostatic pressure does not reduce the hysteresis further, but shifts the martensitic transition close to room temperature. The isothermal entropy change does not depend on warming or cooling protocols and is pressure independent. Experiments in pulsed-magnetic fields on Ni₂Cu_0.21.2In_0.6 find a reversible magnetocaloric effect with a maximum adiabatic temperature change of −13 K.

Of all stoichiometric filled-skutterudite superconductors, LaRu₄As₁₂ has the highest critical field and temperature. Here we report on a detailed Fermi-surface investigation of LaRu₄As₁₂ by means of de Haas–van Alphen measurements and density-functional-theory calculations. We find evidence for a nearly spherical and a multiply connected Fermi-surface sheet. The different effective masses and mass enhancements for the two sheets support two-band superconductivity, which was inferred from previous specific-heat measurements. Furthermore, quantum oscillations persist as well in the superconducting phase. We use two models to describe the additional damping, yielding energy gaps differing by a factor of 5.

Für diesen Vortrag hat keine inhaltliche Kurzangabe vorgelegen.

There are around 200 two-dimensional (2D) networks with different topologies. The structural topology of a 2D network defines its electronic structure. Including the electronic topological properties, it gives rise to Dirac cones, topological flat bands and topological insulators. In this Tutorial Review, we show how electronic properties of 2D networks can be calculated by means of a tight-binding approach, and how these properties change when 2nd-neighbour interactions and spin-orbit coupling are included. We explain how to determine whether or not the resulting electronic features have topological signatures by calculation of Chern numbers, Z2 invariants, and by the nanoribbon approach. This tutorial gives suggestions how such topological properties could be realized in explicit atomistic chemical 2D systems made of molecular frameworks, in particular in 2D polymers, where the edges and vertices of a given 2D net are substituted by properly selected molecular building blocks and stitched together in such a way that long-range π-conjugations is retained.

Efficient manipulations of chiral textures like domain walls and skyrmions are crucial for the development of prospective spintronic devices [1-2]. Domain walls moving in stripes with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction (DMI) exhibit a tilt resulting in a decrease of their maximal velocity [3]. Beside the direct current influence [3], the tilt is usually caused by in-plane fields [4] or an edge roughness [5]. In this work, we show that the domain wall tilt can appear as a result of competition of the in-plane anisotropy and DMI. We also describe the field-driven dynamics of the tilted domain wall.

We consider an infinitely long biaxial stripe with interfacing DMI (Fig. 1) and biaxial anisotropy. The first easy axis of anisotropy is perpendicular to the stripe plane and the second easy axis lies within the stripe plane and makes an angle α with the stripe axis. The shape anisotropy forces α=0, while α≠0 can appear due to other effects, e.g. exchange bias from underlying antiferromagnet. The second anisotropy rotates the in-plane magnetization inside the domain wall according to the in-plane easy axis direction. The optimum of the DMI energy is reached when the magnetization rotates perpendicularly to the domain wall plane. In stripes the energy balance between these two energy terms and the energy of the domain wall tension results in a unidirectional tilt by angle χ of the domain wall plane (χ=0 corresponds to the domain wall perpendicular to the stripe), determined by α. There is a metastable state of the wall, tilted into the opposite direction in a certain range of anisotropy and DMI values. This is related to the symmetry break between the two opposite directions of the magnetization rotation inside the domain wall due to the presence of a weak DMI. Furthermore, the dynamics of the domain wall in the presence of a biaxial anisotropy and DMI exhibits a symmetry break with respect to the magnetic field and the easy axis direction A. The domain wall reveals fast and slow motion regimes for the opposite signs of α. The slow regime is characterized by a smaller Walker field b and switch of the magnetization direction inside the domain wall in a certain field below b . The latter results in an increase of the domain wall speed. The velocity of the domain wall is inversely proportional to cos χ. The maximum of the Walker field corresponds to α≠0 (Fig. 2).

In conclusion, we describe a unidirectional tilt of a domain wall in a biaxial stripe with DMI, which appears at equilibrium without external magnetic field and demonstrate the enhancement of the Walker field and velocity [6]. The domain wall dynamics reveal fast and slow regimes depending on the orientation of the easy axis of the in-plane anisotropy and the applied magnetic field.

References: [1] K.-S. Ryu, L. Thomas, S.-H. Yang et al., Nat. Nanotech., Vol. 8, 527 (2013); [2] O. Pylypovskyi, D. Sheka, V. Kravchuk et al., Sci. Rep. Vol. 6, 23316 (2016); [3] O. Boulle, S. Rohart, L. Buda-Prejbeanu et al., Phys. Rev. Lett. Vol. 111, 217203 (2013); [4] C. Muratov, V. Slastikov, A. Kolesnikov et al., Phys. Rev. B. Vol. 96, 134417 (2017); [5] E. Martinez, S. Emori, N. Perez et al. J. Appl. Phys. Vol. 115, 213909 (2014); [6] O. Pylypovskyi, V. Kravchuk, O. Volkov et al., ArXiv, 2001.03408 (2020)

Skyrmions attract a special attention for spintronic and spinorbitronic devices by their unique static and dynamic properties [1]. The interplay between geometry and magnetization texture gives additional degrees of freedom in control of such topologically nontrivial patterns via geometry-induced anisotropy and Dzyaloshinskii-Moria interaction (DMI) in materials with easy-normal anisotropy [2-5]. It is sufficient for appearance of skyrmions and skyrmion lattices as a ground state on small curvilinear defects [6].

Here, we propose a new way to stabilize skyrmions and control their size via curvature gradient in a nanoindentation even without intrinsic DMI [7]. Our mathematical formalism also allows to describe planar films with inhomogeneous distribution of material parameters. We consider a thin membrane with easy-normal anisotropy and circular nanoindentation of a conic frustrum shape with inner and outer radii R and R , respectively. This geometry can be described by two principal curvatures, k and k , providing the whole information about geometry in the given point of the membrane. While k (r) is inversely proportional to the distance from origin r, k (r) has sharp peaks in points of the bend of the membrane. To compare textures in curved membranes and flat films we propose a projection of a surface of revolution to a plane, which reconstructs a skyrmion equation. The energy of the magnetic texture in projected coordinates obtains a curvature-modified anisotropy and two DMI terms, related to principal curvatures. In contrast to the planar case, the corresponding skyrmion equation is characterized not only by DMI coefficients itself, but also their spatial derivatives playing a role of the external driving force, proportional to d(k + k )/dr. The main consequences of the driving force are: (i) the ground state cannot be strictly normal to the membrane with nonconstant curvature; (ii) a gradient of k can result in stabilization of the Neel skyrmion of radius R or R (Fig. 1). Skyrmions, stabilized at the inner and outer bends, have the opposite chiralities. If the difference between R and R is large enough, both skyrmions can coexist forming a skyrmionium state with zero total winding number. In the limiting case of sharp bends, the minimal angle α of the indentation side for stabilizing topologically nontrivial textures equals 4L/R radians, with R being either R or R (α = 0 corresponds to a flat film) and L being a magnetic length. Numerical analysis of skyrmion stability is performed in a wide range of geometrical parameters (Fig. 2). It is shown that the strength and spatial localization of the DMI coefficient, associated with k , plays the main role in the pinning of topologically nontrivial textures and pinning strength is estimated to be hundredths of Kelvin for typical parameters of Co/Pt multilayers.

In conclusion, we propose a mathematical framework which allows us to describe magnetic nanomembranes with rotational symmetry and planar films with circular distribution of material parameters using the same apparatus. It uncovers two mechanisms of skyrmion stabilization, namely DMI-driven [8] and DMI gradient-driven [7]. The first one does not require the curvature gradients and lead to formation of small-radius skyrmions, while the second allows stabilization of large-radius skyrmions and skyrmionium states of the geometrically defined size.

References: [1] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mater., Vol. 2, 17031 (2017); [2] R. Streubel, P. Fischer, F. Kronast et al., J. Phys. D: Appl. Phys. Vol. 49, 363001 (2016); [3] O. Pylypovskyi, V. Kravchuk, D. Sheka et al., Phys. Rev. Lett. Vol. 114, 197204 (2015); [4] Y. Gaididei, V. Kravchuk, D. Sheka, Phys. Rev. Lett. Vol. 112, 257203 (2014); [5] Y. Gaididei, A. Goussev, V. Kravchuk et al., J. Phys. A: Mat. and Theor. Vol. 50, 385401 (2017); [6] V. Kravchuk, D. Sheka, A. Kákay et al., Phys. Rev. Lett. Vol. 120, 067201 (2018); [7] O. Pylypovskyi, D. Makarov, V. Kravchuk et al., Phys. Rev. Appl. Vol. 10, 064057 (2018); [8] V. Kravchuk, U. Roessler, O. Volkov et al., Phys. Rev. B, Vol. 94, 144402 (2016).

The identification of areas prone to landslides is essential to adapt the response and reduce the negative impact in affected regions. This is usually done using landslide susceptibility models, which give the likelihood of a landslide occurring in an area depending on the local terrain conditions and the location of known past events. Detailed databases covering different thematic groups such as geomorphology, hydrology, geology and land use are paramount in order to produce a reliable identification of susceptible areas. However, thematic data from developing countries are scarce and the situation is even worse in mountainous regions which are yet highly vulnerable to natural disasters such as landslides. As a result, susceptibility models often rely heavily on geomorphic parameters derived from DEMs. The three dominantly used variables include slope, aspect and curvature. While these variables are simple to compute and can be obtained from any GIS software, the geomorphological significance of the last two of them is often poorly justified as the window of observation (3×3 pixels) is too small to capture the morphometric signature of landslides or the overall morphology of an entire slope profile.

This study explores the use of advanced geomorphic indices as the main input for landslide susceptibility models. These indices have been often used in tectonic geomorphology to understand the relationship between surface processes and landscape evolution and can provide a useful way to characterize the topography in mountainous regions. Tested indices include surface roughness, local relief, topographic position index, elevation relief ratio, surface index and Eigen-based analysis of the landscape. The test area encompasses the mountainous areas in Tajikistan (SW Tien Shan and Western Pamir), where large magnitude historical landslides have been reported and studied. Landslide susceptibility maps with good predictive capabilities are obtained using different statistically based approaches such as logistic regression and random forest. First, we explored the spatial association between the variables and the landslide catalog. Then, the input variables are recursively selected for each model based on the spatial associations and the improvement in model performance. The best model is chosen based on its predictive capability, measured by the receiver operator curve (ROC) and its dispersion from the cross-validation. Our results suggest that landslide susceptibility modeling using advanced geomorphic indices as the primary source of thematic information is a viable approach. Measures of the relative importance of geomorphic variables used in the best models show that indices such as eigenvalues, local relief, surface roughness, slope, topographic position index and surface index contributed significantly to the models while commonly used aspect and curvatures had a limited impact. Also, the methodology we used is low cost and built on free and open source programs (R and Python), making it easily available for developing countries.

What should you know about publishing within an EC project? Which license is the best for your publication? The presentation gives information about Open Access and financing of Articles Processing Charges (APC), licencing and the HZDR repositories ROBIS and RODARE.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications.1 Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used as templates for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. In order to investigate the transport properties of the fabricated nanostructures, the wires are contacted using top-down methods. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K.2 Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade behavior at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

Ion beam irradiation of vertical nanopillar structures may be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

Mit dem Ziel, das Publizieren von Artikeln, Forschungsdaten und wissenschaftlicher Software gemäß den FAIR-Prinzipien (https://www.go-fair.org/fair-principles/) zu unterstützen, wurde am HZDR ein integriertes Publikationsmanagement aufgebaut. Insbesondere Daten- und Softwarepublikationen erfordern die Entwicklung bedarfsgerechter organisatorischer und technischer Strukturen ergänzend zu bereits sehr gut funktionierenden Services im Publikationsmanagement. In der Zusammenarbeit mit Wissenschaftlern des HZDR und internationalen Partnern in ausgewählten Projekten wurde der Bedarf an Unterstützung im Forschungsdatenmanagement analysiert. Darauf aufbauend wurde schrittweise ein integriertes System von Infrastrukturen und Services entwickelt und bereitgestellt. In einer seit Mai 2018 gültigen Data Policy wurden die Rahmenbedingungen und Regelungen sowohl für wissenschaftliche Mitarbeiter als auch für externe Messgäste definiert. Im Vortrag wird auf die Erfahrungen im integrierten Publikationsmanagement für Artikel, Forschungsdaten und Forschungssoftware eingegangen und daraus resultierend werden die nächsten Aufgaben und Ziele entwickelt

The usage of ion beam irradiation on vertical nanopillar structures is a prerequisite for fabricating a CMOS-compatible, vertical gate-all-around(GAA) SET device. 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 amorphization 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 as well as Electron Beam Diffraction confirmed the crystallinity of the substrate and nanopillars after HT-irradiation. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm has been observed at higher fluencies. As the original pillar diameter is comparable to the size of the collision cascade, instead of direct knock-on sputtering, enhanced forward sputtering through the sidewalls of the pillar is responsible for this effect. The relation between ion beam energy, flux and temperature with the observed thinning of the nanopillars has been studied experimentally and compared to TRI3DYN simulations. Such a reliable and CMOS-compatible process could serve as a potential downscaling technique for large-scale fabrication of nanopillar-based electronics.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior.
Transistor like devices showed Coulomb blockade behavior at RT.
The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade behavior at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

A Spectroscopic Study of the Interactions of Trivalent f-Elements with α-Chitin and its Constituents

Sorption of Trivalent f-Elements by Materials of Biological Origin: NMR and Luminescence Spectroscopic Studies

This invited lecture gives an overview to students of chemistry at Universidad de Alcalá (Spain) about radiochemistry and the ways to tackle radioactive waste

The Ion Beam Center (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a unique user facility with decades of experience applying ion beams for materials analysis and modification. The IBC provides ion beams of nearly all stable elements in an unique energy range from some tens of eV up to 60 MeV using tandem accelerators and electrostatic ion implanters, focused ion beam systems, a helium ion microscope, highly-charged ions systems, as well as an accelerator mass spectrometer (AMS) and a secondary ion spectrometer combined with a tandem accelerator. Annually, the IBC offers more than 16.000 hours of beam time for research and industrial purposes to users across the globe. Continuous access to the IBC is permitted via an online proposal procedure [1, 2]. In addition to the beam time, the IBC provides numerous add-on services including sample preparation, clean-room processing, surface and thin film metrology, optical and electron-beam lithography, thermal processing, thin-film deposition, optical and electrical characterization, electron microscopy and spectroscopy, X-ray investigations, as well as simulation of ion-related processes and data evaluation.
Since 2011, the spin-off HZDR Innovation GmbH [3] shares the IBC equipment and offers fast and direct access to the IBC for commercial services. The activity of the spin-off is focused on the high-energy ion implantation mostly for doping and defect engineering of semiconductors. Up to 8 inch wafers are handled (semi-)automatically at accelerators of IBC under clean room conditions. Many leading international microelectronic companies are customers of HZDR Innovation GmbH. HZDR Innovation GmbH provides an important contribution to the development and production of novel techniques for micro and power electronics, making semiconductor devices more effective and climate-friendly.

[1] http://www.hzdr.de/db/Cms?pNid=3249
[2] https://gate.hzdr.de/user/
[3] http://hzdr-innovation.de/2/

Graphene and its allotropes belong to the new generation of materials. Due to their extraordinary electrical, mechanical and other properties, their application possibilities are vast. In this work, a study on interactions of graphene oxide (GO) layers using Au and Ga ions with energy of 40 keV was realized. Very shallow layers of GO are modified as low energy ions are depositing energy mostly in the upper layer due to the low projected ion ranges at most of 50 nm. The ion irradiation fluences of 5.0 × 10¹⁴ cm⁻², 5.0 × 10¹⁵ cm⁻² and 5.0 × 10¹⁶ cm⁻² were used. Upon irradiation, the modified GO foils were characterised using nuclear analytical methods – Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA) and various conventional analytical methods such as Raman spectroscopy, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and 2-point conductivity measurements. Oxygen species removal was evidenced as the increasing function of the ion implantation fluence and oxygen depth profiles exhibited complex behaviour connected to implanted ion specie. The deep oxygen depletion in the broad surface layer accompanied by Ga diffusion into the depth was observed in Ga irradiated GO compared to Au irradiated samples which exhibited a narrow oxygen depleted layer at GO surface. XPS evidenced strong increase of C=C bonds compared to C-O bonds on the irradiated GO surface with increasing ion fluence, which was comparable for both ion species. Raman spectroscopy shows the modification of main phonon modes identified in GO. The D peak slight decrease and broadening was observed for GO irradiated with ion fluence above 5 × 10¹⁵ cm⁻² and mainly for Au ion irradiation. FTIR analysis proved the oxygen containing functional group release with the increased ion fluence, mainly C-O group release after Au ion irradiation was observed. Simultaneously H-O stretching absorption peak is in FTIR spectrum reduced more significantly for Ga irradiated GO which is in accordance with RBS elemental analysis exhibiting the more pronounced hydrogen depletion. Electrical conductivity measurement shows the linear I-V characteristics for the GO irradiated using both ion species and all ion fluences; the surface layer exhibited conductive behaviour comparing to pristine GO non-linear I-V characteristics.

In direct sampling for the conditional simulation of random fields with continues distributions the probablity of finding exact matches of the local conditions in the training image is zero. We thus need to take samples with similar but different patterns. The maximum permissible difference is an algorithmic threshold parameter t controlling the speed, the reliability and the correctness of the simulation.

The contribution describes the effect that simulations sampled with this algorithm follow a conditional distribution, which is systematically biased with respect to the conditional distribution represented by the training images. This sampling bias is create by the fact that it is more likely to find conditioning events deviating from the observed conditioning shifted in the direction of the gradient of the marginal density of the conditioning events. These conditioning events however also typically have a conditional distribution shifted accordingly. The implicitly generated distribution of the conditional simulation is thus just not only (as it was always understood) a little smoothness with respect to the true distribution, but systematically biased. This sampling bias can be easily demostrated in simple Gaussian examples, where it introduces a regression to the mean type effect into a conditional simulation. The effect of the bias accumulates along the simulation path. The size of the sampling bias depends on the choosen tolerance, the choosen neighbourhood, the choosen iteration limit, and the local conditioning events.

The contribution will also discuss strategies to limit and control the effect of this sampling bias, by selecting appropriate algorithmic parameters, and by quantifying the DS sampling bias.

The orientation of a chiral magnetic domain wall in a racetrack determines its dynamical properties. In equilibrium, magnetic domain walls are expected to be oriented perpendicular to the stripe axis. We demonstrate the appearance of a unidirectional domain wall tilt in out-of-plane magnetized stripes with biaxial anisotropy and Dzyaloshinskii--Moriya interaction (DMI). The tilt is a result of the interplay between the in-plane easy-axis anisotropy and DMI. We show that the additional anisotropy and DMI prefer different domain wall structure: anisotropy links the magnetization azimuthal angle inside the domain wall with the anisotropy direction in contrast to DMI, which prefers the magnetization perpendicular to the domain wall plane. Their balance with the energy gain due to domain wall extension defines the equilibrium magnetization the domain wall tilting. We demonstrate that the Walker field and the corresponding Walker velocity of the domain wall can be enhanced in the system supporting tilted walls.

Research at the Institute of Ion Beam Physics and Materials Research

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that either the millisecond range flash lamp annealing (solid phase epitaxy) or nanosecond range pulsed laser annealing (liquid phase epitaxy) is able to recrystallized the implanted layers and electrically activate the dopants.The carrier concentration in the heavily doped p- and n-type GaAs with sub-second annealing treatment is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained ultra-highly GaAs films display a room-temperature plasma frequency above 2200 cm-1, which enables to exploit the plasmonic properties of GaAs for sensing in the mid-infrared spectral range.

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low electron effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that both the millisecond range flash lamp annealing (solid phase epitaxy) and nanosecond range pulsed laser annealing (liquid phase epitaxy) are able to recrystallize the implanted layers and electrically activate dopants. The carrier concentration in the heavily doped p- and n-type GaAs is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained GaAs films display a room-temperature plasma frequency above 2200 cm-1, which makes GaAs attractive for sensing in the mid-infrared spectral range.

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I review the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely $\approx 0.4~$mJ/m$^2$, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)

Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters. In these materials magnetic states can be manipulated via electric field and vice versa, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).

Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).