2019, Sivasankaran, R.P., Rockstroh, N., Kreyenschulte, C.R., Bartling, S., Lund, H., Acharjya, A., Junge, H., Thomas, A., Brückner, A.

MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroyscopy, X-ray photoelectron spectroscopy, electron microscopy, photoluminescence, and in situ electron paramagnetic resonance spectroscopy. During photodeposition, the 2H MoS2 phase was formed upon reduction of [MoS4]2− by photogenerated conduction band electrons and then deposited on the surface of CN. A thin crystalline layer of 2H MoS2 formed an intimate interfacial contact with CN that favors charge separation and enhances the photocatalytic activity. The 2H MS-CN phase showed the highest photocatalytic H2 evolution rate (2342 µmol h−1 g−1, 25 mg catalyst/reaction) under UV-vis light irradiation in the presence of lactic acid as sacrificial reagent and Pt as cocatalyst.

2020, Park, G.-H., Reichlova, H., Schlitz, R., Lammel, M., Markou, A., Swekis, P., Ritzinger, P., Kriegner, D., Noky, J., Gayles, J., Sun, Y., Felser, C., Nielsch, K., Goennenwein, S.T.B., Thomas, A.

We report a robust anomalous Nernst effect in Co2MnGa thin films in the thickness regime between 20 and 50 nm. The anomalous Nernst coefficient varied in the range of -2.0 to -3.0 μV/K at 300 K. We demonstrate that the anomalous Hall and Nernst coefficients exhibit similar behavior and fulfill the Mott relation. We simultaneously measure all four transport coefficients of the longitudinal resistivity, transversal resistivity, Seebeck coefficient, and anomalous Nernst coefficient. We connect the values of the measured and calculated Nernst conductivity by using the remaining three magnetothermal transport coefficients, where the Mott relation is still valid. The intrinsic Berry curvature dominates the transport due to the relation between the longitudinal and transversal transport. Therefore, we conclude that the Mott relationship is applicable to describe the magnetothermoelectric transport in Weyl semimetal Co2MnGa as a function of film thickness.

2017, Boehnke, A., Martens, U., Sterwerf, C., Niesen, A., Huebner, T., Von Der Ehe, M., Meinert, M., Kuschel, T., Thomas, A., Heiliger, C., Münzenberg, M., Reiss, G.

Spin caloritronics studies the interplay between charge-, heat- and spin-currents, which are initiated by temperature gradients in magnetic nanostructures. A plethora of new phenomena has been discovered that promises, e.g., to make wasted heat in electronic devices useable or to provide new read-out mechanisms for information. However, only few materials have been studied so far with Seebeck voltages of only some microvolt, which hampers applications. Here, we demonstrate that half-metallic Heusler compounds are hot candidates for enhancing spin-dependent thermoelectric effects. This becomes evident when considering the asymmetry of the spin-split density of electronic states around the Fermi level that determines the spin-dependent thermoelectric transport in magnetic tunnel junctions. We identify Co2FeAl and Co2FeSi Heusler compounds as ideal due to their energy gaps in the minority density of states, and demonstrate devices with substantially larger Seebeck voltages and tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B-based junctions.

2018, Schürmann, M., Shepheard, N., Frese, N., Geishendorf, K., Sudhoff, H., Gölzhäuser, A., Rückert, U., Kaltschmidt, C., Kaltschmidt, B., Thomas, A.

In this manuscript, we first reveal a simple ultra violet laser lithographic method to design and produce plain tailored multielectrode arrays. Secondly, we use the same lithographic setup for surface patterning to enable controlled attachment of primary neuronal cells and help neurite guidance. For multielectrode array production, we used flat borosilicate glass directly structured with the laser lithography system. The multi layered electrode system consists of a layer of titanium coated with a layer of di-titanium nitride. Finally, these electrodes are covered with silicon nitride for insulation. The quality of the custom made multielectrode arrays was investigated by light microscopy, electron microscopy and X-ray diffraction. The performance was verified by the detection of action potentials of primary neurons. The electrical noise of the custom-made MEA was equal to commercially available multielectrode arrays. Additionally, we demonstrated that structured coating with poly lysine, obtained with the aid of the same lithographic system, could be used to attach and guide neurons to designed structures. The process of neuron attachment and neurite guidance was investigated by light microscopy and charged particle microscopy. Importantly, the utilization of the same lithographic system for MEA fabrication and poly lysine structuring will make it easy to align the architecture of the neuronal network to the arrangement of the MEA electrode.. In future studies, this will lead to multielectrode arrays, which are able to specifically attach neuronal cell bodies to their chemically defined electrodes and guide their neurites, gaining a controlled connectivity in the neuronal network. This type of multielectrode array would be able to precisely assign a signal to a certain neuron resulting in an efficient way for analyzing the maturation of the neuronal connectivity in small neuronal networks.

2018, Fernández, J.G., Martínez, V.V., Thomas, A., de la Prida Pidal, V.M., Nielsch, K.

First Order Reversal Curve (FORC) analysis has been established as an appropriate method to investigate the magnetic interactions among complex ferromagnetic nanostructures. In this work, the magnetization reversal mechanism of bi-segmented nanowires composed by long Co and Ni segments contacted at one side was investigated, as a model system to identify and understand the FORC fingerprint of a two-step magnetization reversal process. The resulting hysteresis loop of the bi-segmented nanowire array exhibits a completely different magnetic behavior than the one expected for the magnetization reversal process corresponding to each respective Co and Ni nanowire arrays, individually. Based on the FORC analysis, two possible magnetization reversal processes can be distinguished as a consequence of the ferromagnetic coupling at the interface between the Ni and Co segments. Depending on the relative difference between the magnetization switching fields of each segment, the softer magnetic phase induces the switching of the harder one through the injection and propagation of a magnetic domain wall when both switching fields are comparable. On the other hand, if the switching fields values differ enough, the antiparallel magnetic configuration of nanowires is also possible but energetically unfavorable, thus resulting in an unstable magnetic configuration. Making use of the different temperature dependence of the magnetic properties for each nanowire segment with different composition, one of the two types of magnetization reversal is favored, as demonstrated by FORC analyses.