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138 results on '"Niermann Tore"'

5. Nanosecond Electron Holography by Interference Gating

Author

Wagner, Tolga, Niermann, Tore, Urban, Felix, and Lehmann, Michael

Subjects
Physics - Applied Physics, Physics - Optics
Abstract

The interference gating is a novel method for robust time-resolved electron holographic measurements by directly switching the interference. Here, a new arrangement is presented in which a biprism in the condenser aperture as a fast electric phase shifter is used to control the interference pattern. High-frequency stimulation of the electric phase shifter in the gigahertz range are performed and observed via electron holography, proving the feasibility of interference gating in the upper picosecond range. Despite the bandwidth limitation of 180~MHz of the current signal generator, a time resolution of 100 nanoseconds is achieved through forward correction of the control signal. With this time resolution, it is already possible to measure the transient response of the biasing holder system. Our method paves the way towards a closer look on fast dynamic processes with high temporal and spatial resolution.

Published
2024
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7. Holographic Vector Field Electron Tomography of Three-Dimensional Nanomagnets

Author

Wolf, Daniel, Biziere, Nicolas, Sturm, Sebastian, Reyes, David, Wade, Travis, Niermann, Tore, Krehl, Jonas, Warot-Fonrose, Benedicte, Büchner, Bernd, Snoeck, Etienne, Gatel, Christophe, and Lubk, Axel

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Data Analysis, Statistics and Probability, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

Complex 3D magnetic textures in nanomagnets exhibit rich physical properties, for example in their dynamic interaction with external fields and currents, and play an increasing role for current technological challenges such as energy-efficient memory devices. To study these magnetic nanostructures including their dependency on geometry, composition and crystallinity, a 3D characterization of the magnetic field with nanometer spatial resolution is indispensable. Here we show how holographic vector field electron tomography can reconstruct all three components of magnetic induction as well as the electrostatic potential of a Co/Cu nanowire with sub 10\,nm spatial resolution. We address the workflow from acquisition, via image alignment to holographic and tomographic reconstruction. Combining the obtained tomographic data with micromagnetic considerations we derive local key magnetic characteristics, such as magnetization current or exchange stiffness, and demonstrate how magnetization configurations, such as vortex states in the Co-disks, depend on small structural variations of the as-grown nanowire., Comment: 10 pages, 4 figures

Published
2019
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8. Three-dimensional composition and electric potential mapping of III-V core-multishell nanowires by correlative STEM and holographic tomography

Author

Wolf, Daniel, Hübner, René, Niermann, Tore, Sturm, Sebastian, Prete, Paola, Lovergine, Nico, Büchner, Bernd, and Lubk, Axel

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The non-destructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in 3D but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential - MIP) and space charges. In this letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual <111> oriented GaAs-AlGaAs core-multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram, enables us to observe functional potentials at the NW surfaces and at the Au-NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.

Published
2018
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10. Dislocation-free Ge Nano-crystals via Pattern Independent Selective Ge Heteroepitaxy on Si Nano-Tip Wafers.

Author

Niu, Gang, Capellini, Giovanni, Schubert, Markus Andreas, Niermann, Tore, Zaumseil, Peter, Katzer, Jens, Krause, Hans-Michael, Skibitzki, Oliver, Lehmann, Michael, Xie, Ya-Hong, von Känel, Hans, and Schroeder, Thomas

Subjects
Nanotechnology, Bioengineering, Biochemistry and Cell Biology, Other Physical Sciences
Abstract

The integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. The Si-tip wafers feature a rectangular array of nanometer sized Si tips with (001) facet exposed among a SiO2 matrix. These wafers were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based on nucleation theory predict that the selective growth occurs close to thermodynamic equilibrium, where condensation of Ge adatoms on SiO2 is disfavored due to the extremely short re-evaporation time and diffusion length. The growth selectivity is ensured by the desorption-limited growth regime leading to the observed pattern independence, i.e. the absence of loading effect commonly encountered in chemical vapor deposition. The growth condition of high temperature and low deposition rate is responsible for the observed high crystalline quality of the Ge islands which is also associated with negligible Si-Ge intermixing owing to geometric hindrance by the Si nano-tip approach. Single island as well as area-averaged characterization methods demonstrate that Ge islands are dislocation-free and heteroepitaxial strain is fully relaxed. Such well-ordered high quality Ge islands present a step towards the achievement of materials suitable for optical applications.

Published
2016

11. Photodetection in Hybrid Single-Layer Graphene/Fully Coherent Germanium Island Nanostructures Selectively Grown on Silicon Nanotip Patterns

Author

Niu, Gang, Capellini, Giovanni, Lupina, Grzegorz, Niermann, Tore, Salvalaglio, Marco, Marzegalli, Anna, Schubert, Markus Andreas, Zaumseil, Peter, Krause, Hans-Michael, Skibitzki, Oliver, Lehmann, Michael, Montalenti, Francesco, Xie, Ya-Hong, and Schroeder, Thomas

Subjects
germanium, selective epitaxy, elastic relaxation, graphene, photodetection, Chemical Sciences, Engineering, Nanoscience & Nanotechnology
Abstract

Dislocation networks are one of the most principle sources deteriorating the performances of devices based on lattice-mismatched heteroepitaxial systems. We demonstrate here a technique enabling fully coherent germanium (Ge) islands selectively grown on nanotip-patterned Si(001) substrates. The silicon (Si)-tip-patterned substrate, fabricated by complementary metal oxide semiconductor compatible nanotechnology, features ∼50-nm-wide Si areas emerging from a SiO2 matrix and arranged in an ordered lattice. Molecular beam epitaxy growths result in Ge nanoislands with high selectivity and having homogeneous shape and size. The ∼850 °C growth temperature required for ensuring selective growth has been shown to lead to the formation of Ge islands of high crystalline quality without extensive Si intermixing (with 91 atom % Ge). Nanotip-patterned wafers result in geometric, kinetic-diffusion-barrier intermixing hindrance, confining the major intermixing to the pedestal region of Ge islands, where kinetic diffusion barriers are, however, high. Theoretical calculations suggest that the thin Si/Ge layer at the interface plays, nevertheless, a significant role in realizing our fully coherent Ge nanoislands free from extended defects especially dislocations. Single-layer graphene/Ge/Si-tip Schottky junctions were fabricated, and thanks to the absence of extended defects in Ge islands, they demonstrate high-performance photodetection characteristics with responsivity of ∼45 mA W(-1) and an Ion/Ioff ratio of ∼10(3).

Published
2016

13. Nanofabrication of spin-transfer torque devices by a PMMA mask one step process: GMR versus single layer devices

Author

Parge, Anne, Niermann, Tore, Seibt, Michael, and Münzenberg, Markus

Subjects
Condensed Matter - Materials Science
Abstract

We present a method to prepare magnetic spin torque devices of low specific resistance in a one step lithography process. The quality of the pillar devices is demonstrated for a standard magnetic double layer device. For single layer devices, we found hysteretic switching and a more complex dynamical excitation pattern in higher fields. A simple model to explain the resistance spikes is presented., Comment: 22 pages, 6 figures, submitted to J. Appl. Phys

Published
2006
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22. Advanced Coherent X-ray Diffraction and Electron Microscopy of Individual InP Nanocrystals on Si Nanotips for III-V-on-Si Electronics and Optoelectronics

Author

Niu, Gang, Leake, Steven John, Skibitzki, Oliver, Niermann, Tore, Carnis, Jerome, Kießling, Felix, Hatami, Fariba, Hussein, Emad Hameed, Schubert, Markus Andreas, Zaumseil, Peter, Capellini, Giovanni, Masselink, William Ted, Ren, Wei, Ye, Zuo-Guang, Lehmann, Michael, Schülli, Tobias, Schroeder, Thomas, Richard, Marie-Ingrid, Niu, Gang, Leake, Steven John, Skibitzki, Oliver, Niermann, Tore, Carnis, Jerome, Kießling, Felix, Hatami, Fariba, Hussein, Emad Hameed, Schubert, Markus Andrea, Zaumseil, Peter, Capellini, Giovanni, Masselink, William Ted, Ren, Wei, Ye, Zuo-Guang, Lehmann, Michael, Schülli, Tobia, Schroeder, Thoma, and Richard, Marie-Ingrid

Published
2019

26. Holographic vector field electron tomography of three-dimensional nanomagnets

Author

Wolf, Daniel, primary, Biziere, Nicolas, additional, Sturm, Sebastian, additional, Reyes, David, additional, Wade, Travis, additional, Niermann, Tore, additional, Krehl, Jonas, additional, Warot-Fonrose, Benedicte, additional, Büchner, Bernd, additional, Snoeck, Etienne, additional, Gatel, Christophe, additional, and Lubk, Axel, additional

Published
2019
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28. Advanced Coherent X-ray Diffraction and Electron Microscopy of Individual InP Nanocrystals on Si Nanotips for III-V-on- Si Electronics and Optoelectronics

Author

Niu, Gang, primary, Leake, Steven John, additional, Skibitzki, Oliver, additional, Niermann, Tore, additional, Carnis, Jerome, additional, Kießling, Felix, additional, Hatami, Fariba, additional, Hussein, Emad Hameed, additional, Schubert, Markus Andreas, additional, Zaumseil, Peter, additional, Capellini, Giovanni, additional, Masselink, William Ted, additional, Ren, Wei, additional, Ye, Zuo-Guang, additional, Lehmann, Michael, additional, Schülli, Tobias, additional, Schroeder, Thomas, additional, and Richard, Marie-Ingrid, additional

Published
2019
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29. Precise determination of polarization fields in c-plane GaN/Al x Ga1-x N/GaN heterostructures with capacitance–voltage-measurements

Author

Susilo, Norman, primary, Schilling, Marcel, additional, Narodovitch, Michael, additional, Yao, Hsin-Hung, additional, Li, Xiaohang, additional, Witzigmann, Bernd, additional, Enslin, Johannes, additional, Guttmann, Martin, additional, Roumeliotis, Georgios G., additional, Rychetsky, Monir, additional, Koslow, Ingrid, additional, Wernicke, Tim, additional, Niermann, Tore, additional, Lehmann, Michael, additional, and Kneissl, Michael, additional

Published
2019
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33. Accurate determination of polarization fields in (0 0 0 1) c-plane InAlN/GaN heterostructures with capacitance-voltage-measurements

Author

Susilo, Norman, primary, Roumeliotis, Georgios G, additional, Narodovitch, Michael, additional, Witzigmann, Bernd, additional, Rychetsky, Monir, additional, Neugebauer, Silvio, additional, Guttmann, Martin, additional, Enslin, Johannes, additional, Dadgar, Armin, additional, Niermann, Tore, additional, Wernicke, Tim, additional, Strittmatter, André, additional, Lehmann, Michael, additional, Papadimitriou, Dimitra N, additional, and Kneissl, Michael, additional

Published
2018
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38. Nanofabrication of spin-transfer torque devices by a polymethylmethacrylate mask one step process: Giant magnetoresistance versus single layer devices.

Author

Parge, Anne, Niermann, Tore, Seibt, Michael, and Münzenberg, Markus

Subjects
ROTATIONAL motion, POLYMETHYLMETHACRYLATE, MAGNETORESISTANCE, HYSTERESIS, ELECTRIC resistance, MAGNETISM
Abstract

We present a method to prepare magnetic spin torque devices of low specific resistance in a one step lithography process. The quality of the pillar devices is demonstrated for a standard magnetic double layer device. For single layer devices, we found hysteretic switching and a more complex dynamical excitation pattern in higher fields. A simple model to explain the resistance spikes is presented. [ABSTRACT FROM AUTHOR]

Published
2007
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40. Control of Switching Modes and Conductance Quantization in Oxygen Engineered HfOxbased Memristive Devices

Author

Sharath, Sankaramangalam Ulhas, primary, Vogel, Stefan, additional, Molina-Luna, Leopoldo, additional, Hildebrandt, Erwin, additional, Wenger, Christian, additional, Kurian, Jose, additional, Duerrschnabel, Michael, additional, Niermann, Tore, additional, Niu, Gang, additional, Calka, Pauline, additional, Lehmann, Michael, additional, Kleebe, Hans-Joachim, additional, Schroeder, Thomas, additional, and Alff, Lambert, additional

Published
2017
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46. Selective Epitaxy of InP on Si and Rectification in Graphene/InP/Si Hybrid Structure

Author

Niu, Gang, primary, Capellini, Giovanni, additional, Hatami, Fariba, additional, Di Bartolomeo, Antonio, additional, Niermann, Tore, additional, Hussein, Emad Hameed, additional, Schubert, Markus Andreas, additional, Krause, Hans-Michael, additional, Zaumseil, Peter, additional, Skibitzki, Oliver, additional, Lupina, Grzegorz, additional, Masselink, William Ted, additional, Lehmann, Michael, additional, Xie, Ya-Hong, additional, and Schroeder, Thomas, additional

Published
2016
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47. (Invited) Silicon Nano-Tip Pattern Approach for Surface and Interface Engineering of Fully Coherent, High Ge Content Nanostructure Arrays for High Performance Photodetection

Author

Niu, Gang, primary, Capellini, Giovanni, additional, Lupina, Grzegorz, additional, Niermann, Tore, additional, Salvalaglio, Marco, additional, Marzegalli, Anna, additional, Schubert, Markus Andreas, additional, Zaumseil, Peter, additional, Krause, Hans-Michael, additional, Skibitzki, Oliver, additional, Lehmann, Michael, additional, Montalenti, Francesco, additional, Xie, Ya-Hong, additional, and Schroeder, Thomas, additional

Published
2016
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49. Capping of rare earth silicide nanowires on Si(001)

Author

Appelfeller, Stephan, primary, Franz, Martin, additional, Kubicki, Milan, additional, Reiß, Paul, additional, Niermann, Tore, additional, Schubert, Markus Andreas, additional, Lehmann, Michael, additional, and Dähne, Mario, additional

Published
2016
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50. Local Estimation Of Lattice Parameters

Author

Niermann, Tore, Plüschke, Dennis, Park, Jae Bum, and Lehmann, Michael

Abstract

Mc 2009. Microscopy Conference, Graz, Austria. 30 August - 4 September 2009. First Joint Meeting Of Dreiländertagung And Multinational Congress On Microscopy.

Published
2009
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