Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

34121 Publications

Preparation and Characterization of Solar Thermal Absorbers by Nanoimprint Lithography and Sputtering

Mitteramskogler, T.; Haslinger, M. J.; Wennberg, A.; Fernandez Martínez, I.; Muehlberger, M.; Krause, M.; Guillén, E.

Selective solar absorbers comprised of plasmonic materials offer great flexibility in design along with a highly promising optical performance. However, the nanopattern generation, typically done with electron beam writing, is a very time-intensive process. In this work, we present a fast, scalable, and flexible method for the fabrication of plasmonic materials by the combination of a deposition mask prepared by nanoimprint lithography and thin film deposition by magnetron sputtering. The fabrication process was first performed on silicon wafer substrates using AFM and SEM measurements to calibrate the deposition time, determine maximal deposition height, and characterize samples. Afterwards, the process was transferred to polished Inconel NiCr-alloy substrates used in high temperature solar absorbers. To investigate the adhesion properties of the nanostructure on the substrate, two different deposition methods were investigated: DC magnetron sputtering and High Power Impulse Magnetron Sputtering (HiPIMS).

Keywords: Solar absorbers; nanoimprint lithography; HiPIMS

  • Contribution to proceedings
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA
    MRS Advances 4(2019)35, 1905-1911: Cambridge
    DOI: 10.1557/adv.2019.285
  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Pheonix, USA

Permalink: https://www.hzdr.de/publications/Publ-30516
Publ.-Id: 30516


High temperature in-air stability of solar absorber coatings based on aluminium titanium oxynitride nanocomposites

Heras, I.; Krause, M.; Rincón, G.; Guillén, E.; Azkona, I.; Lungwitz, F.; Munnik, F.; Escobar Galindo, R.

One of the major challenges in Concentrating Solar Power (CSP) implies an increase of the working temperature of the solar receiver. In particular, current central tower systems operate at maximum temperatures of 550 ºC mainly due to the severe degradation that the state of the art absorber paints (i.e. Pyromark®) suffer at higher temperatures. In previous works [1,2] aluminum titanium oxynitrides AlyTi1-y(OxN1-x) were shown to be excellent candidate materials for solar selective coatings (SSC). These results confirmed that the designed SSCs based on materials withstand breakdown at 600 ºC in air after 900 hours of thermal cycling.
In this paper we discuss the high temperature (up to 700ºC) stability in air of a solar absorber coating based on AlyTi1-y(OxN1-x) deposited by cathodic vacuum arc (CVA) at higher working pressure (P = 2.1 Pa) than those discussed in [1] and [2]. The composition, morphology and microstructure of the films were characterized by ion beam analysis, scanning and transmission electron microscopy and X-ray diffraction. The optical properties were determined by ellipsometry and spectrophotometry (UV-Vis-NIR, FTIR). The microstructural and morphological characterization shows the formation of a solid solution of AlTiN crystalline nanoparticles embedded in an amorphous Al2(O, N)3 matrix. This particular microstructure results in a coating with a high absorption coefficient within the whole wavelength range of interest (0,3 to 25 um) as modeled by spectroscopic ellipsometry. Hence, this single layer absorber shows a solar absorptance, α, of 92% and an emissivity, εRT, of 70%. The addition of an antireflective Al2O3 layer and post deposition thermal treatments improved the optical properties of the absorber to better values (α=96% and εRT=60%) than those of Pyromark®. The thermal stability in air of the absorber was firstly analyzed by cyclic heating tests, showing no degradation after 300h of cycles in air at 700ºC. Subsequently, the samples were tested in a solar furnace at 650 °C and 800 ºC for 12 hours at environmental conditions. Therefore, this absorber coating can be a feasible alternative to absorber paints for next generation of concentrated solar power plants operating at high temperature.
[1] I. Heras et al., Sol. Energy Mat. Solar Cells, 176, 81-92 (2018)
[2] R. Escobar-Galindo et al., Sol. Energy Mat. Solar Cells, 185, 183-191 (2018)

Keywords: Solar selective coatings; thermal stability; optical properties; concentrated solar power; optical simulation; oxynitrides

  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30515
Publ.-Id: 30515


ESUO - The European Synchrotron and FEL User Organisation

Arčon, I.; Arikan, P.; Bittencourt, C.; Boscherini, F.; Braz Fernandes, F. M.; Brooks, N.; Casu, B.; D'Astuto, M.; Feiters, M.; Froideval, A.; Granroth, S.; Gross, S.; Gutt, C.; Hase, T.; Jablonska, K.; Jergel, M.; Khan, A.; Kirm, M.; Kokkinidis, M.; Kövér, L.; Lamba, D.; Larsen, H. B.; Lechner, R. T.; Le Hir, R.; Logan, D.; López, O.; Lorentz, K.; Mariani, C.; Marinkovic, B.; Mcguinness, C.; Meedom Nielsen, M.; Micetic, M.; Mickevicius, S.; Mikulík, P.; Petukhov, A.; Pietsch, U.; Pokroy, B.; Purans, J.; Renault, L.; Santoro, G.; Shivachev, B.; Stangl, J.; Tromp, M.; Vankó, G.; Freire Anselmo, A. S.; Blasetti, C.; Grobosch, M.; Helm, M.; Schramm, B.; Vollmer, A.

The European Synchrotron and free-electron laser User Organisation (ESUO) established in 2010 represents about 22.000 users. It is composed of 30 member countries. Our vision is to support a thriving (European) synchrotron and FEL user community with equal opportunities of access and participation for all scientists, based solely on the scientific merit of their ideas.

  • Poster
    11th Joint BER II and BESSY II User Meeting, 04.-06.12.2019, HZB, Germany

Permalink: https://www.hzdr.de/publications/Publ-30514
Publ.-Id: 30514


Cluster tool for in situ processing and comprehensive characterization of energy materials at high temperatures

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

In situ processing and comprehensive characterization is essential for design and development of materials used and processed at high-temperatures. Here, a new cluster tool for processing and depth-resolved compositional, structural and optical characterization of layered
materials with thicknesses ranging from sub-nm to 1 μm at temperatures of -100 to 1000 °C is described [1]. The implemented techniques comprise
magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy and spectroscopic ellipsometry. The combination of techniques enables sample processing by scalable, clean, waste-free, and industry-relevant technologies, quantitative depth-profiling for elements with Z ≥ 6, structural and chemical characterization, sensitivity and nm-precise thickness and optical information for single layers, multilayers and composites. In this study, the cluster tool was used for i) metal-induced crystallization with layer-exchange of a-Si/ Ag layer stacks, and ii) for hightemperature characterization of two types of solar-selective coatings for concentrated solar power (CSP), namely Al Ti (O N )-based single and multilayers [2, 3] and an n-type doped solar-selective transparent conductive oxide [4]. Starting with an a-Si/ Ag bilayer stack, metal-induced silicon crystallization with partial layer exchange occurs at 540 °C. The final stack is approximately described by the sequence crystalline Si (c-Si)/ Ag/ c-Si. All the layers contain minor fractions of the other element. Moreover, the Si volume fraction comprises approximately 10 % of amorphous Si. For the CSP coatings, no compositional and structural changes were found up to a maximum temperature of 840 °C in vacuum. Both types of solar-selective coatings thus represent promising materials for the next generation of CSP technology.
[1] R. Wenisch et al., Anal. Chem. 90, 7837-7824 (2018)
[2] I. Heras et al., Sol. Energy Mat. Solar Cells, 176, 81-92 (2018)
[3] R. Escobar-Galindo et al., Sol. Energy Mat. Solar Cells, 185, 183-191 (2018)
[4] F. Lungwitz et al., submitted (2018)
Financial support by the EU, grant No. 645725, project FRIENDS , and the HGF via the W3 program (S.G.) is gratefully acknowledged.

Keywords: Cluster tool; in situ processing and analysis; high temperature; Rutherford backscattering; Raman spectroscopy; ellipsometry; metal-induced crystallization

  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30511
Publ.-Id: 30511


Acoustic signatures of the phase transitions in the antiferromagnet U2Rh2Sn

Gorbunov, D.; Andreev, A. V.; Ishii, I.; Prokes, K.; Suzuki, T.; Zherlitsyn, S.; Wosnitza, J.

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.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30510
Publ.-Id: 30510


Easy-plane magnetic anisotropy in layered GdMn2Si2 compound with easy-axis magnetocrystalline anisotropy

Gerasimov, E. G.; Terentev, P. B.; Gubkin, A. F.; Fischer, H. E.; Gorbunov, D.; Mushnikov, N. V.

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 TGd < 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.

Permalink: https://www.hzdr.de/publications/Publ-30509
Publ.-Id: 30509


Wayforlight: The Catalogue of European Light Sources

Blasetti, C.; Andrian, I.; Billè, F.; Coghetto, E.; Deiuri, S.; Favretto, D.; Turcinovich, M.; Pugliese, R.; Osmenaj, E.; Appleby, G.; Froideval, A.; Pietsch, U.; Sanchez, A.; Valls Vidal, N.; Mitchell, E.; Rabhi, N.; Aogaki, S.; Kasik, Z.; Canova, F.; Gliksohn, F.; Stozno, D.; Michel, J.; Normand, D.; Brancaleon, R.; Paro, G.; Tinta, M.; Zotti, D.

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.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30507
Publ.-Id: 30507


REELS and Auger spectroscopy study of layers exchange in C/Ni-bilayer system

Vretenár, V.; Janke, D.; Vanco, L.; Krause, M.

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.

Keywords: Metal-induced crystallization; turbostratic carbon; electron spectroscopy

  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30506
Publ.-Id: 30506


Time- and temperature-resolved in situ investigation of the metal-induced crystallization of amorphous carbon thin films

Janke, D.; Julin, J.; Hübner, R.; Gemming, S.; Rafaja, D.; Krause, M.

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.

Keywords: Cluster Tool; in situ processing and analysis; layer exchange; turbostratic carbon

  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30505
Publ.-Id: 30505


Directionality and energetics of the metal-induced crystallization of amorphous carbon thin films

Janke, D.; Wüstefeld, C.; Julin, J. A.; Hübner, R.; Grenzer, J.; Gemming, S.; Rafaja, D.; Krause, M.

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.

  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich
  • Lecture (Conference)
    MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30503
Publ.-Id: 30503


Theory and simulation on nonlinear spin-wave dynamics in magnetic vortices

Körber, L.; Schultheiß, K.; Hula, T.; Verba, R.; Kakay, A.; Hache, T.; Ivanov, B.; Faßbender, J.; Schultheiß, H.

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.

Keywords: nonlinear; spin wave; magnon; vortex; three-magnon scattering; BLS; micromagnetic simuations; micromagnetism

  • Poster
    710. WE-Heraeus-Seminar: Spin Transport in Complex Magnetic Structures, 07.-10.01.2020, Physikzentrum Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-30502
Publ.-Id: 30502


Integration of 1D and 2D Materials into Functional Structures and Devices

Georgiev, Y.

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.

Keywords: 1D materials; 2D materials; semiconductor nanowires; DNA origami; transition metal dichalcogenides; top-down nanofabrication; bottom-up nanofabrication; junctionless nanowire transistors; reconfigurable field effect transistors; band-to-band tunnel field effect transistors

  • Invited lecture (Conferences)
    Meeting at the Advanced Microelectronic Centre Aachen (AMICA), AMO gGmbH, 02.-03.12.2019, Aachen, Germany

Permalink: https://www.hzdr.de/publications/Publ-30499
Publ.-Id: 30499


Ion beam implanted Germanium nanowires

Echresh, A.; Xie, Y.; Prucnal, S.; Rebohle, L.; Georgiev, Y.

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.

Keywords: Ion beam implantation; Flash lamp annealing; Doping; p-n junction; Infrared sensor

  • Poster
    45th International Conference on Micro & Nano Engineering (MNE), 23.-26.09.2019, Rhodes, Greece
  • Poster
    NanoNet International Conference 2019, 08.-11.10.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30498
Publ.-Id: 30498


Phosphorous doped Germanium nanowires

Echresh, A.; Jazavandi Ghamsari, S.; Georgiev, Y.; Rebohle, L.

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.

  • Poster
    DPG Spring Meeting 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30497
Publ.-Id: 30497


Ion beam implanted Germanium nanowires fabricated by using electron beam lithography

Echresh, A.; Jazavandi Ghamsari, S.; Helm, M.; Rebohle, L.; Georgiev, Y.

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.

  • Poster
    Towards Reality in Nanoscale Materials X, 14.-16.02.2019, Levi, Finland

Permalink: https://www.hzdr.de/publications/Publ-30495
Publ.-Id: 30495


Implementation of a cryogenic hydrogen jet target at the DRACO PW laser

Rehwald, M.; Bernert, C.; Curry, C.; Cowan, T.; Gauthier, M.; Glenzer, S.; Goede, S.; Kim, J.; Kluge, T.; Kraft, S.; Obst-Hübl, L.; Schoenwaelder, C.; Schlenvoigt, H.-P.; Schramm, U.; Ziegler, T.; Zeil, K.

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.

  • Lecture (Conference)
    4th Targetry for High Repetition Rate Laser-Driven Sources Workshop, 09.-12.06.2019, Milano, Italien

Permalink: https://www.hzdr.de/publications/Publ-30494
Publ.-Id: 30494


Hybrid LWFA-PWFA staging; from concept to proof-of-principle experiments

Irman, A.; Bussmann, M.; Chang, Y.-Y.; Corde, S.; Couperus Cabadağ, J. P.; Debus, A.; Ding, H.; Döpp, A.; Heinemann, T.; Hidding, B.; Gilljohann, M. F.; Götzfried, J.; Karsch, S.; Kononenko, O.; Kurz, T.; Köhler, A.; Martinez De La Ossa, A.; Pausch, R.; Raj, G.; Schindler, S.; Schöbel, S.; Zarini, O.; Assmann, R. W.; Schramm, U.

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.

Keywords: laser wakefield acceleration; plasma wakefield acceleration

  • Open Access Logo Lecture (Conference)
    European Advanced Accelerator Concept (EAAC), 20.09.2019, ELBA, Italia

Permalink: https://www.hzdr.de/publications/Publ-30492
Publ.-Id: 30492


Field driven recovery of the collective spin dynamics of the chiral soliton lattice

Trindade Goncalves, F. J.; Shimamoto, Y.; Sogo, T.; Paterson, G. W.; Kousaka, Y.; Togawa, Y.

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.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30491
Publ.-Id: 30491


Laser-proton acceleration from a cryogenic hydrogen jet at the DRACO PW laser

Rehwald, M.; Bernert, C.; Curry, C.; Cowan, T.; Gauthier, M.; Glenzer, S.; Goede, S.; Kim, J.; Kluge, T.; Kraft, S.; Obst-Hübl, L.; Schoenwaelder, C.; Schlenvoigt, H.-P.; Schramm, U.; Ziegler, T.; Zeil, K.

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.

  • Lecture (Conference)
    Laser Plasma Accelerator Workshop 2019, 06.05.2019, Split, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-30489
Publ.-Id: 30489


Using XFELs to Probe Extreme Magnetic Fields Inside Solid Targets Driven by Optical High Power Lasers at HiBEF

Huang, L.; Schlenvoigt, H.-P.; Takabe, H.; Cowan, T.

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.

Keywords: magnetic field; X-Ray polarimetry; Faraday rotation; XFEL

  • Invited lecture (Conferences)
    The 4th International Conference on Matter and Radiation at Extremes (ICMRE 2019), 29.05.-02.06.2019, Hefei, China

Permalink: https://www.hzdr.de/publications/Publ-30488
Publ.-Id: 30488


Mutual dependence of oxygen and vacancy diffusion in bcc Fe and dilute iron alloys

Wang, X.; Faßbender, J.; Posselt, M.

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.

Keywords: Ferritic iron alloys; Mutual dependence of oxygen and vacancy diffusion; First-principle calculations; Atomistic Kinetic Monte Carlo simulations; Influence of substitutional atoms

Permalink: https://www.hzdr.de/publications/Publ-30485
Publ.-Id: 30485


Scaling up the Synthesis of a Hydroxyquinoline-Functionalized p‑tert-Butylcalix[4]arene.

Roode-Gutzmer, Q. I.; Holderied, L. N.; Glasneck, F.; Kersting, B.; Fröhlich, P.; Bertau, M.

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.

Keywords: rare earths; lanthanides; actinides; solvent extraction; calixarene synthesis; scale up

Permalink: https://www.hzdr.de/publications/Publ-30484
Publ.-Id: 30484


Characterization of Goethe’s prisms by external ion beam

Munnik, F.; Mäder, M.; Heller, R.; Schreiber, A.; Müller, O.

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.

  • Lecture (Conference)
    16th International Conference on Particle Induced X-ray Emission, 24.-29.03.2019, Caldas da Rainha, Portugal

Permalink: https://www.hzdr.de/publications/Publ-30483
Publ.-Id: 30483


Junctionless Nanowire Transistors: an Excellent Platform for Ultrasensitive Chemo/Biosensors

Georgiev, Y.

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).

Keywords: nanowires; biosensors; junctionless transistors; protein; streptavidin; single-molecule detection

  • Invited lecture (Conferences)
    IHRS NanoNet International Conference, 08.-11.10.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30482
Publ.-Id: 30482


Application of junctionless nanowire transistors as ultrasensitive biosensors

Georgiev, Y.; Petkov, N.; Yu, R.; Nightingale, A. M.; Buitrago, E.; Lotty, O.; Demello, J. C.; Ionescu, A. M.; Holmes, J. D.

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.

Keywords: nanowires; biosensors; junctionless transistors; protein; streptavidin; single-molecule detection

  • Lecture (Conference)
    45th International Conference on Micro- and Nanofabrication and Manufacturing (MNE 2019), 23.-26.09.2019, Rhodes, Greece

Permalink: https://www.hzdr.de/publications/Publ-30481
Publ.-Id: 30481


Group IV Nanowires: Fabrication and Particular Applications

Georgiev, Y.; Khan, M. B.; Deb, D.; Echresh, A.; Ghamsari, S. J.; Prucnal, S.; Rebohle, L.; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.

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.

Keywords: semiconductor nanowires; top-down nanofabrication; electron beam lithography; reactive ion etching; bottom-up nanofabrication; nanoelectronic devices; junctionless nanowire transistors; reconfigurable field effect transistors; biosensors

  • Lecture (Conference)
    83d DPG Annual Conference and DPG Spring Conference, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30479
Publ.-Id: 30479


Fabrication and Particular Applications of Group IV Semiconductor Nanowires

Georgiev, Y.; Khan, M. B.; Deb, D.; Echresh, A.; Jazavandi Ghamsari, S.; Prucnal, S.; Rebohle, L.; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.; Knoch, J.

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.

Keywords: semiconductor nanowires; top-down nanofabrication; bottom-up nanofabrication; nanoelectronic devices; junctionless nanowire transistors; reconfigurable field effect transistors; band-to-band tunnel field effect transistors; biosensors

  • Lecture (Conference)
    The 10th workshop “Towards Reality in Nanoscale Materials X”, 12.-14.02.2019, Levi, Finland

Permalink: https://www.hzdr.de/publications/Publ-30478
Publ.-Id: 30478


Vanishing influence of the band gap on charge exchange of slow highly charged ions in freestanding single layer MoS₂

Creutzburg, S.; Schwestka, J.; Niggas, A.; Inani, H.; Tripathi, M.; George, A.; Heller, R.; Kozubek, R.; Madauß, L.; Facsko, S.; Kotakoski, J.; Schleberger, M.; Turchanin, A.; Grande, P. L.; Aumayr, F.; Wilhelm, R. A.

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.

Permalink: https://www.hzdr.de/publications/Publ-30477
Publ.-Id: 30477


Adaptive Control of Meniscus Velocity in Continuous Caster Based on NARX Neural Network Model

Abouelazayem, S.; Glavinic, I.; Wondrak, T.; Hlava, J.

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.

Keywords: Mining; mineral and metal; Nonlinear system identification; Adaptive control design

  • Contribution to proceedings
    13th IFAC Workshop on Adaptive and Learning Control Systems - ALCOS 2019, 04.-06.12.2019, Winchester, United Kingdom
    IFAC-PapersOnLine 52(2019) 29, 222-227
    DOI: 10.1016/j.ifacol.2019.12.653

Permalink: https://www.hzdr.de/publications/Publ-30476
Publ.-Id: 30476


Control of Jet Flow Angle in Continuous Casting Process using an Electromagnetic Brake

Abouelazayem, S.; Glavinic, I.; Wondrak, T.; Hlava, J.

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.

Keywords: Flow Control; Tomography; Process Automation; Model Predictive Control

  • Contribution to proceedings
    Mining, Mineral and Metal Processing 2019, 28.-30.08.2019, Stellenbosch, South Africa
    Control of Jet Flow Angle in Continuous Casting Process using an Electromagnetic Brake
    DOI: 10.1016/j.ifacol.2019.09.169

Permalink: https://www.hzdr.de/publications/Publ-30475
Publ.-Id: 30475


Two new diffractometers at BM20/ESRF for single crystal, powder and surface diffraction

Hennig, C.; Schmidt, M.; Ikeda-Ohno, A.; Radoske, T.; Feig, M.; Findeisen, S.; Claußner, J.; Exner, J.; Naudet, D.; Baumann, N.; Scheinost, A.

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.

Keywords: Single crystall diffraction; powder diffraction; surface diffraction; Rossendorf Beamline

  • Lecture (Conference)
    Joint Polish-German Crystallographic Meeting 2020, 24.-27.02.2020, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30473
Publ.-Id: 30473


Experimental study on the magnetic pulse welding process of large aluminum tubes on steel rods

Bellmann, J.; Schettler, S.; Dittrich, S.; Lueg-Althoff, J.; Schulze, S.; Hahn, M.; Beyer, E.; Tekkaya, A. E.

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.

Permalink: https://www.hzdr.de/publications/Publ-30471
Publ.-Id: 30471


Near free-fall oscillatory velocities in liquid metal rotating convection

Vogt, T.; Horn, S.; Aurnou, J.

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.

Keywords: Rotating convection; liquid metal; Rayleigh-Bénard convection

  • Lecture (Conference)
    72nd Annual Meeting of the American Physical Society’s Division of Fluid Dynamics (DFD), 23.-27.11.2019, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-30469
Publ.-Id: 30469


Imaging of current induced Néel vector switching in antiferromagnetic Mn2Au

Bodnar, S. Y.; Filianina, M.; Bommanaboyena, S. P.; Forrest, T.; Maccherozzi, F.; Sapozhnik, A. A.; Scurschii, I.; Kläui, M.; Jourdan, M.

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.

Permalink: https://www.hzdr.de/publications/Publ-30467
Publ.-Id: 30467


Cubic symmetry and magnetic frustration on the fcc spin lattice in K2IrCl6

Khan, N.; Prishchenko, D.; Scurschii, I.; Mazurenko, V. G.; Tsurlin, A. A.

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 θCW ≃ −43 K, and the extrapolated saturation field of Hs ≃ 87 T. All these parameters are well reproduced ab initio using Ueff = 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.

Permalink: https://www.hzdr.de/publications/Publ-30466
Publ.-Id: 30466


Electron spin resonance study of spin relaxation in the strong-leg spin ladder with nonmagnetic dilution

Krasnikova, Y. V.; Glazkov, V. N.; Ponomaryov, O.; Zvyagin, S.; Povarov, K. Y.; Galeski, S.; Zheludev, A.

We have studied electron spin resonance (ESR) absorption spectra for the nonmagnetically diluted strongleg spin ladder magnet (C7H10N)2Cu(1−x)ZnxBr4 (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.

Permalink: https://www.hzdr.de/publications/Publ-30465
Publ.-Id: 30465


Investigations on bubbly two-phase flow in a constricted vertical pipe

Neumann-Kipping, M.; Bieberle, A.; Hampel, U.

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.

Keywords: gas-liquid two-phase flow; bubbly flow; flow constriction; three-dimensional flow; computed tomography; experimental benchmark data

Related publications

Downloads:

  • Secondary publication expected from 21.05.2021

Permalink: https://www.hzdr.de/publications/Publ-30464
Publ.-Id: 30464


Atomic Scale Analysis of Ultra-Thin InxGa1-xN/GaN Quantum Wells by High Resolution HR(S)TEM

Vasileiadis, I. G.; Lymperakis, L.; Liebscher, C. H.; Dimakis, E.; Hübner, R.; Adikimenakis, A.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.

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.

  • Lecture (Conference)
    XXXIV Panhellenic Conference on Solid State Physics and Materials Science, 11.09.2019, Patras, Greece

Permalink: https://www.hzdr.de/publications/Publ-30462
Publ.-Id: 30462


Status and Applications TOF-SIMS in the Helium Ion Microscope

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

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

  • Lecture (Conference)
    Ion Beam Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30461
Publ.-Id: 30461


Strain Relaxation in In(Ga)N/GaN Short Period Superlattices

Vasileiadis, I. G.; Adikimenakis, A.; Dimakis, E.; Hübner, R.; Lymperakis, L.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.

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.

  • Lecture (Conference)
    EUROMAT 2019, 01.09.2019, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-30460
Publ.-Id: 30460


Nano-pillar evolution by FIB irradiation with heavy ions

Bischoff, L.; Heinig, K.-H.; Möller, W.; Klingner, N.; Pilz, W.; Borany, J.

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.

  • Lecture (Conference)
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30459
Publ.-Id: 30459


Sub-50 keV helium ions as an imaging probe in transmission microscopy and secondary ion mass spectrometry

Mousley, M.; Eswara, S.; Bouton, O.; Audinot, J.-N.; Klingner, N.; Hlawacek, G.; Wirtz, T.

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).

  • Lecture (Conference)
    Microscopy Conference 2019, 01.-05.09.2019, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30458
Publ.-Id: 30458


Controlled-growth and tuning of electronic properties in GaAs nanowires on Si substrates

Tauchnitz, T.; Balaghi, L.; Fotev, I.; Shan, S.; Pashkin, O.; Bussone, G.; Grifone, R.; Grenzer, J.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.

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.

  • Poster
    2nd Scientific Workshop of the Program “From Matter to Materials and Life” (MML) in the Helmholtz Research Field “Matter”, 13.02.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30457
Publ.-Id: 30457


Complex three-dimensional heterostructures in III-As nanowires

Tauchnitz, T.; Balaghi, L.; Hübner, R.; Wolf, D.; Bussone, G.; Grifone, R.; Grenzer, J.; Pelekanos, N. T.; Schneider, H.; Helm, M.; Dimakis, E.

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.

  • Lecture (Conference)
    20th European Workshop on Molecular Beam Epitaxy, 17.02.2019, Lenggries, Germany

Permalink: https://www.hzdr.de/publications/Publ-30456
Publ.-Id: 30456


TOF-SIMS with highest lateral resolution by pulsing the Ne-GFIS in a HIM

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

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.

  • Lecture (Conference)
    3rd EuFN Workshop 2019 of the European FIB Network, 12.-14.06.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30455
Publ.-Id: 30455


Complex quantum dots in III-As nanowires

Tauchnitz, T.; Balaghi, L.; Hübner, R.; Chatzarakis, N.; Pelekanos, N. T.; Bussone, G.; Grifone, R.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.

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.

Keywords: self-catalyzed; strain engineering; bandgap tuning

  • Lecture (Conference)
    Nanowire Week 2019, 23.09.2019, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-30454
Publ.-Id: 30454


Imaging by Transmission Ion Microscopy and Secondary Ion Mass Spectrometry using sub-50 keV He+ ion beams

Eswara, S.; Mousley, M.; de Castro, O.; Bouton, O.; Audinot, J.-N.; Klingner, N.; Koch, C.; Hlawacek, G.; Wirtz, T.

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).

  • Lecture (Conference)
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-20.10.2019, Antibes, France

Permalink: https://www.hzdr.de/publications/Publ-30453
Publ.-Id: 30453


A TOF-SIMS nanoprobe with sub-10 nm lateral resolution

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

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

  • Poster
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-18.10.2019, Antibes, France

Permalink: https://www.hzdr.de/publications/Publ-30452
Publ.-Id: 30452


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

Kelley, D. H.; Tithof, J. R.; Horstmann, G. M.; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.

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

  • Invited lecture (Conferences)
    Physics seminar, 18.11.2019, Fayetteville, Arkansas, USA

Permalink: https://www.hzdr.de/publications/Publ-30448
Publ.-Id: 30448


Energy cascades & the asymmetric motion of coherent structures

Kelley, G. H.; Tithof, J. R.; Horstmann, G. M.; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.

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

  • Lecture (Conference)
    72nd Annual Meeting of the APS Division of Fluid Dynamics, 23.-26.11.2019, Seattle, Washington, USA

Permalink: https://www.hzdr.de/publications/Publ-30447
Publ.-Id: 30447


Flow regimes of Rayleigh-Bénard convection in a vertical magnetic field

Zürner, T.; Schindler, F.; Vogt, T.; Eckert, S.; Schumacher, J.

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.

Keywords: magnetoconvection Rayleig-Bénard convection; liquid metal

Downloads:

  • Secondary publication expected from 10.01.2021

Permalink: https://www.hzdr.de/publications/Publ-30445
Publ.-Id: 30445


Rayleigh-Bénard Convection in Liquid metal under Influence of Vertical Magnetic Fields

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Conference (Lecture):

American Physics Society (APS) DFD meeting 2019 Seattle

In the presented Rayleigh-Bénard convection experiments the turbulent 3d-
flow of the liquid gallium-indium-tin alloy is investigated by use of ultrasound
Doppler velocimetry, temperature and contactless inductive flow tomography
measurements. We reconstruct for the first time near-wall as well as bulk
flow, momentum and heat transport as well as long-term behaviour of the large-scale liquid
metal flow at a low Prandtl number of 0.029 and high Rayleigh numbers up
to 6 · 10e7. Also the influence of a strong magnetic field on the turbulent liquid metal is investigated. The results of the
experiments are compared to direct numerical simulations and other experiments. These are also
considered for the interpretation of the measured turbulence statistics.
Our experiments aim to provide a deeper understanding of the turbulent
convection and its interaction with magnetic fields in turbulent low Prandtl number
flows as those in molten steel, aluminium or geo- and astrophysical flows.

Keywords: Rayleigh-Bénard convection; magnetohydrodynamics; low Prandtl number; liquid metal; ultrasound velocimetry

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-11-23
    DOI: 10.14278/rodare.231
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30444
Publ.-Id: 30444


Analysis, design and optimization of compact ultra-high sensitivity coreless induction coil sensors

Ratajczak, M.; Wondrak, T.

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.

Keywords: magnetic field measurement; induction coil; gradiometric coil; contactless inductive flow tomography

Permalink: https://www.hzdr.de/publications/Publ-30443
Publ.-Id: 30443


Rayleigh-Bénard Convection in a Vertical Magnetic Field at Low Prandtl Number

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

The present work shows the experimental realisation of three-dimensional
magnetoconvection studies at Rayleigh numbers between 10e6 and 6 · 10e7 and Hartmann
numbers up to 1000 in a Rayleigh-Bénard convection cell. The fluid in the cell is the
GaInSn metal alloy with a low Prandtl number of 0.029. The flow is investigated using
thermocouples and ultrasound-Doppler-velocimetry. The change of the Nusselt number
with increasing Hartmann number is studied and presented. Experimental results are
compared to other experiments and simulations.

Keywords: liquid metal; low Prandtl number; Rayleigh-Bénard magnetoconvection; vertical magnetic Field

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.229
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30441
Publ.-Id: 30441


X-ray radiographic visualization of bubbly flows injected by a top submerged lance in a liquid metal layer

Akashi, M.; Keplinger, O.; Anders, S.; Reuter, M.; Eckert, S.

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.

Keywords: Two phase flow; Liquid metal; Top submerged lance

  • Lecture (Conference)
    17th Multiphase Flow Conference and Short Course, 11.-15.11.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30440
Publ.-Id: 30440


Low Prandtl Number Rayleigh-Bénard Convection in a Vertical Magnetic Field

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Lecture (Conference)

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

We are investigating turbulent Rayleigh-Bénard convection in liquid metal under the
influence of a vertical magnetic field. Utilizing a combination of thermocouple (TC) and
ultrasound-Doppler-velocimetry (UDV) measurements gives us the possibility to directly
determine the temperature and velocity field, respectively. Further this gives us the
possibility to observe changes in the large-scale flow structure.
By applying magnetic fields to the liquid metal convection, we quantified changes of heat
and momentum transport in the liquid metal alloy GaInSn. The experimental results of our
setup agree well with theory findings and direct numerical simulations of the dynamics in
our convection cell. The requirement of large computing power at these parameters makes
it hard to simulate long-term dynamics with time scales from minutes to several hours. Thus
to investigate slow developing dynamics like sloshing, rotation, or deformation of the large-
scale flow structure model experiments are indispensable.
We demonstrate the suppression of the convective flow by a vertical magnetic field in a
cylindrical cell of aspect ratio 1. In this setup Rayleigh numbers up to 6·107 are
investigated. The flow structure at low Hartmann numbers is a single roll large scale
circulation (LSC). Increasing the Hartmann number leads to a transition from the single-roll
LSC into a cell structure. An even stronger magnetic field supresses the flow in the center
of the cell completely and expels the flow to the side walls.
Even above the critical Hartmann numbers corresponding to the Chandrasekhar limit for
the onset of magnetoconvection in a fluid layer without lateral boundaries we still observe
remarkable flows near the side walls. The destabilising effect of the non-conducting side
walls was predicted by theory and simulations, and is here for the first time experimentally
confirmed.

Keywords: Rayleigh-Bénard-Convection; Magnetohydrodynamic; low Prandtl Number; liquid metal; Ultrasound velocimetry

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.227
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30439
Publ.-Id: 30439


CFD Modeling of Top-Submerged-Lance Argon injection in liquid metal

Obiso, D.; Sebastian, K.; Akashi, M.; Eckert, S.; Reuter, M.

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.

Keywords: two phase flow; top submerged lance; liquid metal

  • Lecture (Conference)
    10th Copper International Conference (COPPER 2019), 18.-21.08.2019, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-30436
Publ.-Id: 30436


Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

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

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.

  • Open Access Logo Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 03.04.2019, Regensburg, Deutschland
    DOI: 10.1063/1.5057733

Permalink: https://www.hzdr.de/publications/Publ-30435
Publ.-Id: 30435


Experimental analysis of gas phase dynamics in a lab scale bubble column operated with deionized water and NaOH solution under uniform bubbly flow conditions

Kipping, R.; Kryk, H.; Hampel, U.

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.

Keywords: bubble column hydrodynamics; mono-dispersed bubbly flow; bubble size distribution; bubble rise velocity; electrolyte solutions; Ultrafast X-ray tomography

Related publications

Downloads:

  • Secondary publication expected from 25.08.2021

Permalink: https://www.hzdr.de/publications/Publ-30434
Publ.-Id: 30434


High-motility visible light-driven Ag/AgCl Janus microswimmers interacting with passive beads

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.; Makarov, D.

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.

Keywords: Active Janus particles; exclusion interaction; passive beads; visible light‐driven micromotors

  • Lecture (Conference)
    DPG Spring Meetings 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30432
Publ.-Id: 30432


Programmed Magnetically-Triggered Ultrafast Soft Robots

Wang, X.; Ge, J.; Canon Bermudez, G. S.; Kosub, T.; Illing, R.; Wang, C.; Bischoff, L.; Faßbender, J.; Makarov, D.

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)

Keywords: Soft robots; magnetic field; ultrafast actuation

  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibit, 22.-26.04.2019, Phoenix, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-30431
Publ.-Id: 30431


Investigation of particle dynamics and solidification in two phase system by neutron radiography

Baranovskis, R.; Sarma, M.; Ščepanskis, M.; Beinerts, T.; Gaile, A.; Eckert, S.; Räbiger, D.; Lehmann, E. H.; Thomsen, K.; Trtik, P.

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.

Keywords: Neutron radiography; particle trapping; directional solidification; mushy zone

  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Magnetohydrodynamics 56(2020)1, 43-50
    DOI: 10.22364/mhd.56.1.4

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30430
Publ.-Id: 30430


Pulsed magnetic field, high pressure and FIB microstructures - a powerful combination for studies of unconventional metals

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    J-Physics Conference, 18.-21.09.2019, Kobe, Japan

Permalink: https://www.hzdr.de/publications/Publ-30428
Publ.-Id: 30428


FIB microstructures and experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    LNCMI - Solid State Physics Seminar, 18.04.2019, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-30427
Publ.-Id: 30427


Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys

Devi, P.; Salazar Mejia, C.; Caron, L.; Singh, S.; Nicklas, M.; Felser, C.

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 Ni2CuxMn1.4−xIn0.6, we obtained a thermal hysteresis of the martensitic phase transition in Ni2Cu0.2Mn1.2In0.6 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 Ni2Cu0.21.2In0.6 find a reversible magnetocaloric effect with a maximum adiabatic temperature change of −13 K.

Permalink: https://www.hzdr.de/publications/Publ-30426
Publ.-Id: 30426


Fermi surface investigation of the filled skutterudite LaRu4As12

Klotz, J.; Götze, K.; Lorenz, V.; Prots, Y.; Rosner, H.; Harima, H.; Bochenek, L.; Henkie, Z.; Cichorek, T.; Sheikin, I.; Wosnitza, J.

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.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30424
Publ.-Id: 30424


Focused-ion-beam assisted micropatterning for experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzangabe vorgelegen.

  • Invited lecture (Conferences)
    Helmholtz MML-Workshop, 13.-15.02.2019, Dresden, Deutschland
  • Invited lecture (Conferences)
    EMFL User Meeting, 25.06.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30423
Publ.-Id: 30423


Topological Two-Dimensional Polymers

Springer, M.; Liu, T.-J.; Kuc, A. B.; Heine, T.

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.

Permalink: https://www.hzdr.de/publications/Publ-30422
Publ.-Id: 30422


Exploring the applications of advanced geomorphic indices in statistically based landslide susceptibility models: a case study from Tajik Tien Shan and Pamir

Barbosa Mejia, L. N.; Andreani, L.; Gloaguen, R.

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.

Keywords: Landslide susceptibility; morphometric indices; digital elevation model

  • Poster
    EGU2019, 10.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30417
Publ.-Id: 30417


Publishing - Licensing - Financing : 1. EU-Day at HZDR

Reschke, E.

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.

Keywords: Open Access; Articles Processing Charges (APC); ROBIS; RODARE; Publishing; European Commission; Project publications; Licensing; Copyright; Hybrid journals; DEAL

  • Open Access Logo Lecture (others)
    1. EU-Day at Helmholtz-Zentrum Dresden-Rossendorf, 09.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30416
Publ.-Id: 30416


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Eychmüller, A.; Samano, E.; Seidel, R.; Erbe, A.

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.

  • Poster
    MML meeting From Matter to Materials and Life, 15.01.2019, Dreikönigskirche Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30415
Publ.-Id: 30415


Morphology Modification of Si Nanopillars under Ion Irradiation at Elevated Temperatures

Xu, X.; Heinig, K.-H.; Möller, W.; Engelmann, H.-J.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; Borany, J.

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.

  • Lecture (Conference)
    10th International Workshop on Nanoscale Pattern Formation at Surfaces (NanoPatterning 2019), 07.-10.07.2019, Surrey, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30414
Publ.-Id: 30414


Integriertes Management und Publikation von wissenschaftlichen Artikeln, Software und Forschungsdaten am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) : 1.Sächsische FDM-Tagung 2019, Dresden

Reschke, E.; Konrad, U.

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

Keywords: ROBIS; RODARE; Publikationsmanagement; Forschungsdaten; Forschungssoftware; publication management; research data; research software; FAIR; Open Access

  • Open Access Logo Invited lecture (Conferences)
    1. Sächsische FDM-Tagung, 19.09.2019, Dresden, Deutschland

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30413
Publ.-Id: 30413


Towards a vertical nanopillar-based single electron transistor – a high-temperature ion beam irradiation approach

Xu, X.; Heinig, K.-H.; Engelmann, H.-J.; Möller, W.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; Borany, J.

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.

  • Lecture (Conference)
    The Second International Workshop of the PicoFIB Network, 13.02.2019, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30412
Publ.-Id: 30412


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Eychmüller, A.; Samano, E.; Seidel, R.; Erbe, A.

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.

  • Lecture (Conference)
    DPG Spring Meeting, 31.03.-05.04.2019, Universität Regensburg, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30411
Publ.-Id: 30411


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Martinez-Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.

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.

  • Lecture (Conference)
    IHRS NanoNET International Conferance, 08.-11.10.2019, Dresden, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30410
Publ.-Id: 30410


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.

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.

  • Open Access Logo Poster
    Nucleic Acid Nanotechnology: from algorithmic design to biochemical applications, 27.-29.05.2019, Aalto University, Finland

Permalink: https://www.hzdr.de/publications/Publ-30409
Publ.-Id: 30409


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

Kammerlander, K.; Huittinen, N. M.; Kaden, P.; Stumpf, T.; Brunner, E.

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

  • Lecture (Conference)
    GdCH Jahrestagung der Fachgruppe Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30408
Publ.-Id: 30408


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

Kammerlander, K.; Köhler, L.; Huittinen, N. M.; Stumpf, T.; Brunner, E.

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

  • Lecture (Conference)
    Migration 2019, 15.-20.09.2019, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-30407
Publ.-Id: 30407


Radiochemistry and the radioactive nuclear waste management

Mayordomo Herranz, N.

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

  • Invited lecture (Conferences)
    Lectures about chemistry (Lecciones de química), 06.02.2020, Alcalá de Henares, Spain

Permalink: https://www.hzdr.de/publications/Publ-30406
Publ.-Id: 30406


Commercial applications of research institute Tandem accelerators: the Rossendorf example

Akhmadaliev, S.

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/

  • Invited lecture (Conferences)
    NUSPRASEN Workshop on Nuclear Science Applications, 25.-27.11.2019, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-30405
Publ.-Id: 30405


Structural and compositional modification of graphene oxide by means of medium and heavy ion implantation

Malinský, P.; Cutroneo, M.; Sofer, Z.; Szőkölová, K.; Böttger, R.; Akhmadaliev, S.; Macková, A.

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.

Keywords: Chemical properties; Electrical properties; Graphene oxide; Ion Irradiation

Permalink: https://www.hzdr.de/publications/Publ-30404
Publ.-Id: 30404


Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction

Pylypovskyi, O.; Kravchuk, V. P.; Volkov, O.; Faßbender, J.; Sheka, D.; Makarov, D.

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.

Keywords: magnetism; doman wall; anisotropy; Dzyaloshinskii-Moriya interaction; Walker field; Walker velocity

Permalink: https://www.hzdr.de/publications/Publ-30401
Publ.-Id: 30401


Materials science for information technology

Helm, M.

Research at the Institute of Ion Beam Physics and Materials Research

Keywords: ion implanation; materials science; information technology

  • Lecture (others)
    talk at UESTC, 15.10.2019, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-30400
Publ.-Id: 30400


Tunable plasmonics in heavily doped GaAs via ion implantation and sub-second annealing

Duan, J.; Wang, M.; Helm, M.; Skorupa, W.; Zhou, S.; Prucnal, S.

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.

Keywords: heavily doped GaAs; plasmonic; sub-second annealing

  • Lecture (Conference)
    2019 DPG, 31.03.-05.04.2019, Regensbrug, Germany

Permalink: https://www.hzdr.de/publications/Publ-30399
Publ.-Id: 30399


Tunable plasmonics in heavily doped GaAs fabricated by ion implantation and sub-second annealing

Juanmei, D.; Helm, M.; Skorupa, W.; Zhou, S.; Prucnal, S.

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.

Keywords: Heavily doped GaAs; mid-infrared plasmonic; sub-second annealing

  • Poster
    2019 Spring Meeting of the European Materials Research Society, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30398
Publ.-Id: 30398


Experimental and Theoretical Studies of Exchange-driven Chiral Effects

Volkov, O.

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)

Keywords: Micromagnetism; curvilinear effects

  • Invited lecture (Conferences)
    Seminar at the Advanced Materials and Microsystems Laboratory, 05.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30397
Publ.-Id: 30397


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.; Makarov, D.

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).

Keywords: Micromagnetism; curvilinear effects; magnetoelectric materials

  • Lecture (Conference)
    2019 MRS Fall meeting & Exhibit, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30396
Publ.-Id: 30396


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.; Makarov, D.

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).

Keywords: Micromagnetism; curvilinear effects; magnetoelectric materials

  • Lecture (Conference)
    2019 Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2019, Las Vegas, USA

Permalink: https://www.hzdr.de/publications/Publ-30395
Publ.-Id: 30395


Theoretical and Experimental Study of Curvature Effects in Nanomagnetism

Volkov, O.

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.

[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)

Keywords: Micromagnetism; curvilinear effects

  • Invited lecture (Conferences)
    Advanced Training Course “Spintronics Radar Detectors”, 14.-18.10.2019, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-30394
Publ.-Id: 30394


Experimental observation of exchange-driven chiral effects in parabolic nanostripes

Volkov, O.

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)

Keywords: Micromagnetism; curvilinear effects

  • Invited lecture (Conferences)
    International Workshop “Curvilinear Magnetism”, 23.-24.05.2019, Kyiv, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-30393
Publ.-Id: 30393


Mesoscale Dzyaloshinskii-Moriya interaction: geometrical tailoring of the magnetochiralit

Volkov, O.; Sheka, D.; Gaididei, Y.; Kravchuk, V.; Rößler, U.; Faßbender, J.; Makarov, D.

Magnetic crystals with broken chiral symmetry possess intrinsic spinorbit driven Dzyaloshinskii-Moriya interaction (DMI). Geometrically broken symmetry in curvilinear magnetic systems also leads to the appearance of extrinsic to the crystal exchange driven effective DMI [1,2]. The interplay between the intrinsic and geometrical-induced DMI paves the way to a mesoscale DMI, whose symmetry and strength depend on the geometrical and material parameters [3]. We demonstrate this approach on the example of a helix with intrinsic DMI. Adjusting the helical geometry allows to create new artificial chiral nanostructures with defined properties from standard magnetic materials. For instance, we propose a novel approach towards artificial magnetoelectric materials, whose state is controlled by means of the geometry.
[1] Y. Gaididei et. al, Phys. Rev. Lett. 112, 257203 (2014).
[2] R. Streubel et. al, J. Phys. D: Applied Physics 49, 363001 (2016).
[3] O. Volkov et. al, Scientific Reports 8, 866 (2018).

Keywords: Micromagnetism; curvilinear effects

  • Open Access Logo Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30392
Publ.-Id: 30392


High-motility visible light-driven Ag/AgCl Janus microswimmers interacting with passive beads

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.; Makarov, D.

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] This is a severe drawback for the applications where the efficient transport of micromotors within a vessel is demanded.

Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The proper design of an 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 (excitation λ = 450-490 nm). The revealed propulsion of micromotors owns a dependence of the intensity of visible light, which is contributed by the couple plasmonic light absorption of Ag/AgCl and the efficient photochemical decomposition of AgCl. With the motion comparisons of individual Janus particle, small cluster, and large cluster, the effect of suppressed rotational diffusion has been revealed experimentally and in numerical simulations. Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] The exclusion efficiency is controlled by the number of single Janus PS/Ag/AgCl particles that compose a cluster. 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 2018, 14, 1803613.
4. Wang, X., et al., Small 2018, 14, 1802537.

Keywords: Active Janus particles; exclusion interaction; passive beads; visible light‐driven micromotors

  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30391
Publ.-Id: 30391


Experimental confirmation of exchange-driven DMI

Volkov, O.; Kakay, A.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Faßbender, J.; Makarov, D.

Dzyaloshinskii-Moriya interaction (DMI) is a key ingredient which allows to obtain chiral non-collinear magnetic textures, e.g. chiral domain walls and skyrmions. The conventional spin-orbit induced DMI emerges in gyrotropic crystals or at the interfaces. Therefore, tailoring of DMI is done by optimizing materials. A viable alternative to the material screening approach relies on the use of geometrically broken symmetries of conventional materials, where local geometrical curvatures generate effective exchange-induced DMI.
Here, we provide the very first experimental confirmation of the existence of the curvature-induced DMI in a Permalloy parabolic nanostripe. By analyzing the evolution of transversal domain wall (DW) [1] under the influence of external field we correlate the depinning field of the DW with the curvature-induced DMI field. We put forth a framework to analyze this field and assess the strength of the effective DMI.
[1] O. Volkov et. al, Physica Status Solidi – Rapid Research Letters, 1800309 (2018).

Keywords: Micromagnetism; curvilinear effects

  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30390
Publ.-Id: 30390


Magnetically-triggered ultrafast soft robots with embedded magnetic cognition and feedback control

Wang, X.; Canon Bermudez, G. S.; Faßbender, J.; Makarov, D.

In the last years, soft robots have been designed and developed to fulfil demands of better malleability and adaptability to changing environment [1-2]. They can be made of various stimuli responsive materials, which respond to 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 their long-range penetration, easy accessibility, and controllability [2, 9, 10] offer exciting advantages. Despite the significant advances in soft magnetic actuators, real-time monitoring and precise feedback control [11-13] remain a challenge for magnetic soft robots.

Here, we present a soft robotic system capable of precisely controlling its deformation degree by means of embedded highly compliant, high-performance magnetic sensors. Our ultrathin (7-100 μm) and ultrafast soft robots that can be actuated by in external magnetic fields pulsating at rates of up to 200 Hz. The high-performance magnetic field sensor is based on the giant magnetoresistive effect and is prepared on ultrathin polymeric foils [14-17] to assure its high mechanical stability combined with mechanical imperceptibility. The latter is crucial to avoid any disturbance of the soft actuator due to the presence of magnetic sensing device. The self-sensing function is realized by monitoring the change of the sensor signal upon approaching it to a magnetic patch applied to the soft robot. This concept of an entirely soft and integrated sensor-actuator system enables contactless self-tracking of motion for magnetic soft robots and can be readily extended to other stimuli-driven soft actuators. These developments will pave the way towards intelligent soft robots, autonomous and reactive soft devices, and new types of human-robot interaction.


[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., Nat Mat. 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nat Mat. 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today 10, 30 (2007)
[7] Q. Zhao et al., Nat Commun 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)
[11] T. G. Thuruthel et al., Sci Robot. 4, eaav1488 (2019)
[12] J. A. Lewis et al., Adv. Mater. 30, 1706383 (2018)
[13] W. Zhang et al., Adv Funct Mater. 29, 1806057 (2019)
[14] M. Melzer et al., Adv. Mater. 27, 1274 (2015)
[15] G. S. C. Bermúdez et al., Nat Electron. 1, 589 (2018)
[16] G. S. C. Bermúdez et al., Sci Adv., 4, eaao2623 (2018)
[17] P. N. Granell et al., npj Flexible Electronics, 3, 3 (2018)

Keywords: Soft robot; magnetic sensor; feedback control

  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30389
Publ.-Id: 30389


Experimental and theoretical study of curvature effects in parabolic nanostripes

Volkov, O.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Kakay, A.; Faßbender, J.; Makarov, D.

Curvilinear magnetic objects are in the focus of intensive research due to the possibility to obtain new fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. The physics in these systems is driven by the interplay between exchange and magnetostatic interactions, which contain spatial derivatives in their energy functionals. This makes both interactions sensitive to the appearance of bends and twists in the physical space.
Here, we address experimentally and theoretically curvature-induced effects in parabolic nanostripes with different geometrical parameters [2]. We show that two different magnetic states can appear: the homogeneous magnetic distribution along the parabolic stripe and a state with a transversal domain wall pinned at the vertex of the parabola. The analytical calculation, based on local magnetostatic model, showed its validity and applicability in a wide range of geometrical parameters.
[1] R. Streubel et al., J. Phys. D: Applied Physics 49, 363001 (2016).
[2] O. Volkov et al., Physica Status Solidi – Rapid Research Letters, 1800309 (2018).

Keywords: Micromagnetism; curvilinear effects

  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30388
Publ.-Id: 30388


Magnetic and Magnetothermal Properties of Hydrogenated Materials Based on Rare Earths and Iron

Paukov, M. A.; Ivanov, L. A.; Gorbunov, D.; Tereshnina, I. S.

Iron-rich rare-earth compounds are the basis for high-energy permanent magnets. These include the R(Fe,T)12, R2Fe17, and R2FeB intermetallics (R = rare earth; T = Ti, V, Mo, Si) that readily absorb hydrogen, which changes their fundamental and functional characteristics. In this letter, we investigate the stability of the magnetic properties of some hydrides with maximum hydrogen content (namely, TmFe11TiH1 and Tm2Fe17H5.5) in a wide temperature range using high magnetic fields. The magnetic phase transition from the ferrimagnetic to the ferromagnetic state was studied immediately after hydrides were obtained, as well as after one year of storage of the samples at ambient temperature. Only the TmFe11TiH hydride is stable over time. The effect of hydrogen on the magnetothermal properties of the Nd2Fe14B and Nd1Pr1Fe14B compounds and a range of magnetic phase transitions were also investigated. Hydrogenation leads to a decrease in the magnetocaloric effect in all investigated compounds as a result of an increase in the distance between magnetically active ions due to the lattice expansion. A magnetic phase diagram is constructed.

Permalink: https://www.hzdr.de/publications/Publ-30387
Publ.-Id: 30387


Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2

Ranjith, K. M.; Luther, S.; Reimann, T.; Schmidt, B.; Schlender, P.; Sichelschmidt, J.; Yasuoka, H.; Strydom, A. M.; Scurschii, I.; Wosnitza, J.; Kühne, H.; Doert, T.; Baenitz, M.

High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without intrinsic disorder, are investigated by magnetization and specific heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance. The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the CP(T ) data, agreeing with a clear Ms/3 plateau of M(H), which is associated with an up-up-down spin arrangement. For the H ǀǀ c direction, a field-induced transition could be evidenced at a much higher field range (9–21 T). The 23Na NMR measurements provide microscopic evidence of field-induced ordering for both directions. A reentrant behavior of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J ≃ 4.7 K and Jz ≃ 2.33 K are extracted from the modified bond-dependent XXZ model for the spin- 1/2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond frustration, arising from the complex spin-orbit entangled 4 f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin- 1/2 triangular-lattice antiferromagnets.

Permalink: https://www.hzdr.de/publications/Publ-30386
Publ.-Id: 30386


Microscopic insights into the disorder induced phase transition in FeRh thin films

Eggert, B.; Schmeink, A.; Potzger, K.; Lindner, J.; Fassbender, J.; Ollefs, K.; Keune, W.; Bali, R.; Wende, H.

By employing 57Fe conversion electron Mössbauer spectroscopy, we qualitatively determined the changes of the microscopic Fe moment of chemical disordered epitaxial B2-FeRh(001) thin films, where the chemical disorder has been induced by ion irradiation with Ne+. Apart from the initial magnetic splitting at 25.4 T an additional sextet contribution arises with an hyperfine field of 27.4 T. A comparison between the structural disorder and the temperature induced phase transition shows a similar change of the 57Fe hyperfine field as a function of the macroscopic magnetisation. This gives an indirect indication, that the metamagnetic phase transition proceeds via a defect-driven domain nucleation of ferromagnetic domains in the antiferromagnetic matrix, as it was suggested based on XPEEM and nano-XRD measurements along the phase transition [1]. We would like to thank the Ion Beam Center at Helmholtz-Zentrum Dresden-Rossendorf for providing the necessary facilities and acknowledge the financial support by DFG (WE2623/17-1).
D. Keavney et al. Scientific Reports 8 1778 (2018)

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

Permalink: https://www.hzdr.de/publications/Publ-30385
Publ.-Id: 30385


Frustrated and low-dimensional magnetic materials in high magnetic fields

Wosnitza, J.

es liegt keine inhaltliche Kurzfassung des Vortrages vor

  • Invited lecture (Conferences)
    VII European-Asian Symposium “Trends in MAGnetism”, EASTMAG 2019,, 08.-13.09.2019, Ekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-30384
Publ.-Id: 30384


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