2022, Borrmann, Fabian, Tsuda, Takuya, Guskova, Olga, Kiriy, Nataliya, Hoffmann, Cedric, Neusser, David, Ludwigs, Sabine, Lappan, Uwe, Simon, Frank, Geisler, Martin, Debnath, Bipasha, Krupskaya, Yulia, Al‐Hussein, Mahmoud, Kiriy, Anton

The understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective “in-water” applications is developed. A combined experimental–theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10−2 S cm−1 under ambient conditions and 10−1 S cm−1 in vacuum. The modeling explains the stabilizing effects for various dopants. The simulations show a significant doping-induced “collapse” of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.

2023, Volkov, Oleksii M., Wolf, Daniel, Pylypovskyi, Oleksandr V., Kákay, Attila, Sheka, Denis D., Büchner, Bernd, Fassbender, Jürgen, Lubk, Axel, Makarov, Denys

Chiral effects originate from the lack of inversion symmetry within the lattice unit cell or sample’s shape. Being mapped onto magnetic ordering, chirality enables topologically non-trivial textures with a given handedness. Here, we demonstrate the existence of a static 3D texture characterized by two magnetochiral parameters being magnetic helicity of the vortex and geometrical chirality of the core string itself in geometrically curved asymmetric permalloy cap with a size of 80 nm and a vortex ground state. We experimentally validate the nonlocal chiral symmetry breaking effect in this object, which leads to the geometric deformation of the vortex string into a helix with curvature 3 μm−1 and torsion 11 μm−1. The geometric chirality of the vortex string is determined by the magnetic helicity of the vortex texture, constituting coupling of two chiral parameters within the same texture. Beyond the vortex state, we anticipate that complex curvilinear objects hosting 3D magnetic textures like curved skyrmion tubes and hopfions can be characterized by multiple coupled magnetochiral parameters, that influence their statics and field- or current-driven dynamics for spin-orbitronics and magnonics.

2020, Bauer, Christoph, Veremchuk, Igor, Kunze, Christof, Benad, Albrecht, Dzhagan, Volodymyr M., Haubold, Danny, Pohl, Darius, Schierning, Gabi, Nielsch, Kornelius, Lesnyak, Vladimir, Eychmüller, Alexander

The n-type semiconductor system Bi2Te3Bi2Se3 is known as a low-temperature thermoelectric material with a potentially high efficiency. Herein, a facile approach is reported to synthesize core/shell heterostructured Bi2Te2Se/Bi2Te3 nanosheets (NSs) with lateral dimensions of 1-3 mu m and thickness of about 50nm. Bi2Te3 and Bi2Se3, as well as heterostructured Bi2Te2Se/Bi2Te3 NSs are obtained via colloidal synthesis. Heterostructured NSs show an inhomogeneous distribution of the chalcogen atoms forming selenium and tellurium-rich layers across the NS thickness, resulting in a core/shell structure. Detailed morphological studies reveal that these structures contain nanosized pores. These features contribute to the overall thermoelectric properties of the material, inducing strong phonon scattering at grain boundaries in compacted solids. NSs are processed into nanostructured bulks through spark plasma sintering of dry powders to form a thermoelectric material with high power factor. Electrical characterization of our materials reveals a strong anisotropic behavior in consolidated pellets. It is further demonstrated that by simple thermal annealing, core/shell structure can be controllably transformed into alloyed one. Using this approach pellets with Bi2Te2.55Se0.45 composition are obtained, which exhibit low thermal conductivity and high power factor for in-plane direction with zT of 1.34 at 400K.

2016, Surrey, Alexander, Schultz, Ludwig, Rellinghaus, Bernd

Nanosized or nanoconfined hydrides are promising materials for solid-state hydrogen storage. Most of these hydrides, however, degrade fast during the structural characterization utilizing transmission electron microscopy (TEM) upon the irradiation with the imaging electron beam due to radiolysis. We use ball-milled MgH2 as a reference material for in-situ TEM experiments under low-dose conditions to study and quantitatively understand the electron beam-induced dehydrogenation. For this, valence electron energy loss spectroscopy (VEELS) measurements are conducted in a monochromated FEI Titan3 80–300 microscope. From observing the plasmonic absorptions it is found that MgH2 successively converts into Mg upon electron irradiation. The temporal evolution of the spectra is analyzed quantitatively to determine the thickness-dependent, characteristic electron doses for electron energies of both 80 and 300 keV. The measured electron doses can be quantitatively explained by the inelastic scattering of the incident high-energy electrons by the MgH2 plasmon. The obtained insights are also relevant for the TEM characterization of other hydrides.

2022, Liu, Lixiang, Huang, Shaozhuan, Shi, Wujun, Sun, Xiaolei, Pang, Jinbo, Lu, Qiongqiong, Yang, Ye, Xi, Lixia, Deng, Liang, Oswald, Steffen, Yin, Yin, Liu, Lifeng, Ma, Libo, Schmidt, Oliver G., Shi, Yumeng, Zhang, Lin

Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional “Swiss-roll” microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe2O3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, and electrochemical evolution of electrodes in real time, allowing us to reveal information that is not accessible with bulk-level characterization techniques.

2021, Nikitin, S.E., Nishimoto, S., Fan, Y., Wu, J., Wu, L.S., Sukhanov, A.S., Brando, M., Pavlovskii, N.S., Xu, J., Vasylechko, L., Yu, R., Podlesnyak, A.

[No abstract available]

2022, Fomin, Vladimir M., Rezaev, Roman O., Dobrovolskiy, Oleksandr V.

Extending of nanostructures into the third dimension has become a major research avenue in condensed-matter physics, because of geometry- and topology-induced phenomena. In this regard, superconductor 3D nanoarchitectures feature magnetic field inhomogeneity, non-trivial topology of Meissner currents and complex dynamics of topological defects. Here, we investigate theoretically topological transitions in the dynamics of vortices and slips of the phase of the order parameter in open superconductor nanotubes under a modulated transport current. Relying upon the time-dependent Ginzburg–Landau equation, we reveal two distinct voltage regimes when (i) a dominant part of the tube is in either the normal or superconducting state and (ii) a complex interplay between vortices, phase-slip regions and screening currents determines a rich FFT voltage spectrum. Our findings unveil novel dynamical states in superconductor open nanotubes, such as paraxial and azimuthal phase-slip regions, their branching and coexistence with vortices, and allow for control of these states by superimposed dc and ac current stimuli.