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- ItemControl of Positive and Negative Magnetoresistance in Iron Oxide : Iron Nanocomposite Thin Films for Tunable Magnetoelectric Nanodevices(2020) Nichterwitz, Martin; Honnali, Shashank; Zehner, Jonas; Schneider, Sebastian; Pohl, Darius; Schiemenz, Sandra; Goennenwein, Sebastian T.B.; Nielsch, Kornelius; Leistner, KarinThe perspective of energy-efficient and tunable functional magnetic nanostructures has triggered research efforts in the fields of voltage control of magnetism and spintronics. We investigate the magnetotransport properties of nanocomposite iron oxide/iron thin films with a nominal iron thickness of 5-50 nm and find a positive magnetoresistance at small thicknesses. The highest magnetoresistance was found for 30 nm Fe with +1.1% at 3 T. This anomalous behavior is attributed to the presence of Fe3O4-Fe nanocomposite regions due to grain boundary oxidation. At the Fe3O4/Fe interfaces, spin-polarized electrons in the magnetite can be scattered and reoriented. A crossover to negative magnetoresistance (-0.11%) is achieved at a larger thickness (>40 nm) when interface scattering effects become negligible as more current flows through the iron layer. Electrolytic gating of this system induces voltage-triggered redox reactions in the Fe3O4 regions and thereby enables voltage-tuning of the magnetoresistance with the locally oxidized regions as the active tuning elements. In the low-magnetic-field region (<1 T), a crossover from positive to negative magnetoresistance is achieved by a voltage change of only 1.72 V. At 3 T, a relative change of magnetoresistance about -45% during reduction was achieved for the 30 nm Fe sample. The present low-voltage approach signifies a step forward to practical and tunable room-temperature magnetoresistance-based nanodevices, which can boost the development of nanoscale and energy-efficient magnetic field sensors with high sensitivity, magnetic memories, and magnetoelectric devices in general. Copyright © 2020 American Chemical Society.
- ItemAnalysis of the Annealing Budget of Metal Oxide Thin-Film Transistors Prepared by an Aqueous Blade-Coating Process(Weinheim : Wiley-VCH, 2022) Tang, Tianyu; Dacha, Preetam; Haase, Katherina; Kreß, Joshua; Hänisch, Christian; Perez, Jonathan; Krupskaya, Yulia; Tahn, Alexander; Pohl, Darius; Schneider, Sebastian; Talnack, Felix; Hambsch, Mike; Reineke, Sebastian; Vaynzof, Yana; Mannsfeld, Stefan C. B.Metal oxide (MO) semiconductors are widely used in electronic devices due to their high optical transmittance and promising electrical performance. This work describes the advancement toward an eco-friendly, streamlined method for preparing thin-film transistors (TFTs) via a pure water-solution blade-coating process with focus on a low thermal budget. Low temperature and rapid annealing of triple-coated indium oxide thin-film transistors (3C-TFTs) and indium oxide/zinc oxide/indium oxide thin-film transistors (IZI-TFTs) on a 300 nm SiO2 gate dielectric at 300 °C for only 60 s yields devices with an average field effect mobility of 10.7 and 13.8 cm2 V−1 s−1, respectively. The devices show an excellent on/off ratio (>106), and a threshold voltage close to 0 V when measured in air. Flexible MO-TFTs on polyimide substrates with AlOx dielectrics fabricated by rapid annealing treatment can achieve a remarkable mobility of over 10 cm2 V−1 s−1 at low operating voltage. When using a longer post-coating annealing period of 20 min, high-performance 3C-TFTs (over 18 cm2 V−1 s−1) and IZI-TFTs (over 38 cm2 V−1 s−1) using MO semiconductor layers annealed at 300 °C are achieved.
- ItemAtom size electron vortex beams with selectable orbital angular momentum(London : Nature Publishing Group, 2017) Pohl, Darius; Schneider, Sebastian; Zeiger, Paul; Rusz, Ján; Tiemeijer, Peter; Lazar, Sorin; Nielsch, Kornelius; Rellinghaus, BerndThe decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging – both of which are prerequisites for future atomic EMCD investigations.