DPC-STEM is a scanning transmission electron microscopy technique capable of imaging electric and magnetic field structures of a TEM specimen. Furthermore, the integrated DPC (iDPC) signal offers the possibility to rather easily image light elements (even hydrogen atoms) which are otherwise very hard to detect within a (S)TEM. Thus, by combining DPC measurements with other high-resolution (S)TEM imaging and spectroscopy techniques new insights into the relationship between (chemical) structure and electric or magnetic domain configurations can be gained.
In this talk I will briefly introduce the basic ideas behind the measurement principle and how we applied the technique to explore the relationship between the chemical micro- and the magnetic domain structure of two spinodally decomposed ferromagnetic alloys (Cu52Ni34Fe14 and Fe54Cr31Co15). Furthermore, I will discuss our investigations of multiferroic (doped) BiFeO3 thin films and how we can use DPC STEM to detect and directly image oxygen vacancies within a doped Bi0.8Ca0.2Fe0.95Mg0.05O3 thin film. Finally, I will briefly talk about the challenges of acquiring, processing and interpreting DPC data.
Wearable sensors allow for the monitoring of human physiology not only in laboratory conditions but also during everyday activity. Ultrasound transducers represent an emerging class of wearable sensors. The key component of a conventional US transducer is a piezoceramic crystal which converts an electrical signal into mechanical oscillations to generate US waves that propagate deep into the tissues and convert the echoes back. However, the piezoceramic is hardly acceptable for integration into the skin-wearable device because of its stiffness, acoustic impedance mismatch (which requires using a gel for standard probes), high processing temperatures, and complexity of the fabrication process.
This talk reports the progress in the fabrication of a fully-printed single-channel organic flexible ultrasound transducer. We will discuss screen and inkjet printing approaches and the effects of printed pattern morphology and geometry on transducer oscillation characteristics. Also, the possible ways of tuning the resonance frequency for the medical range will be demonstrated.
The Earth’s magnetosheath consists of turbulent, shocked solar wind (SW) plasma. Magnetosheath jets are dynamic pressure enhancements which are frequently observed within this region. They travel anti-sunward from the bow shock to the Earth’s magnetopause and can be geoeffective. While several generation mechanisms have been proposed, jets are generally linked to processes at the quasi-parallel bow shock and the foreshock. Our goal is to analyze, how these jets are related to large-scale SW structures, in particular coronal mass ejections (CMEs) as well as stream interaction regions (SIRs) and associated high speed streams (HSSs). We use jets detected by the THEMIS spacecraft between 2008 to 2020. The number of detected jets is lower during the passing of CMEs. Significantly more jets are observed during SIRs and HSSs. We find that jets are unlikely to appear during a mix of low Alfvén Mach numbers and high IMF cone angles, which are SW conditions often found during CMEs and their associated sheaths. These conditions may inhibit the formation of a well-defined foreshock and therefore affecting the jet generation.
Earth’s dipole magnetic field shields the planet from the constantly flowing stream of solar wind and high-energy particles. The solar wind is deflected around this magnetic barrier and leads to a variety of different plasma processes. One such process governing the energy transfer across the magnetopause is the Kelvin-Helmholtz instability (KHI), excited by the velocity shear between the fast- flowing deflected solar wind (magnetosheath) plasma and the relatively stagnant magnetosphere. It has been frequently observed during periods of northward interplanetary magnetic field (IMF), however much less is known about its behaviour during southward IMF conditions.
In this talk we will sketch the interaction between the solar wind and Earth’s magnetosphere and explain fundamental plasma effects governed by this interaction. We will further examine the multi-scale and multi-process character of these interactions and obtain a basic understanding of the spacecraft missions studying these effects. Fully kinetic PIC simulations will additionally shed light on the plasma studies performed at Earth’s magnetopause.
The Earth's magnetosphere is formed by the interaction between the intrinsic dipole field and the solar wind, into which the interplanetary magnetic field (IMF) is frozen. Magnetic Reconnection, a process during which the magnetic topology suddenly changes and large amounts of energy are converted and transferred to the ambient plasma, plays a key role in this context. In the Earth's environment, this process has extensively been studied by several multipoint missions, such as NASA's Magnetospheric Multiscale (MMS) and ESA's Cluster mission. These in-situ observations showed that magnetic reconnection takes place not only at large-scale stable magnetopause or magnetotail current sheets but also in transient localized current sheet features.
Recently, an event study suggested magnetic reconnection taking place at one particular Dipolarization Front (DF) event. DFs are considered as transient magnetic boundary structures that are embedded into fast earthward-propagating plasma flows in the Magnetotail. They exhibit a sharp increase in the northward magnetic field component and a steep density gradient across, separating hot and tenuous plasma from cold and dense plasma.
In this work this unique DF event was investigated further using MMS data to confirm magnetic reconnection taking place. To study the context of the reconnection event, we investigate data from MMS as well as from Cluster, which observed this DF event only 15s earlier, about 2.1 RE dawnward of MMS. Ion plasma data from MMS and Cluster showed opposite flows in dawn-dusk direction, indicating a flow diversion and associated vortex flow structures, with MMS and Cluster located in oppositely oriented vortices. These multi-point data suggest that this unique DF-associated reconnection event results not from a simple earthward propagation of the DF but from a more globally diverging and rotating flow in the near-Earth magnetotail.
Tatiana Kormilina: Analytic Electron Tomography of CuNiFe Magnetic Spinodal Alloys.
Thomas Boné: Periodic Stripes of Charged and Uncharged Molecules Induced by Self-Assembling Nanostructures
Max Niederreiter: On the Structure of Tetracyanoethylene on Cu(111)
Florian Schwarz: STM Investigation of 2H-DPP on Iron Oxides
Nikola Simic: Phase Analysis of (Li)FePO4 by Selected Area Electron Diffraction in Transmission Electron Microscopy