Browsing by Author "Richter, Gunther"

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Open Access
Charakterisierung der Keimbildung und des Wachstums dünner Pd-Schichten auf der SrTiO3(001)-Oberfläche
(2000) Richter, Gunther; Rühle, Manfred (Prof. Dr.)
Mit dieser Arbeit liegt Studie vor, die das Wachstum von Pd auf SrTiO3(001) von der Keimbildung bis zum Spätstadium der Inselkoaleszenz quantitativ beschreibt. Unter den untersuchten Bedingungen zeigt Pd immer Inselwachstum. Auch bei hoher Übersättigung und niedriger Aufdampftemperatur ließ sich kein Lagenwachstum beobachten. In Abhängigkeit der Temperatur stellten sich unterschiedliche Orientierungsbeziehungen ein. Bei niedrigen Temperaturen unterhalb bildeten sich Pd-Schichten mit einer {111}-Fasertextur. Für hohe Wachstumstemperaturen und niedrige Aufdampfraten ergibt sich ein epitaktisches Wachstum. Aus der Gleichgewichtsgestalt der epitaktischen Inseln konnte durch eine Wulff-Konstruktion die Grenzflächenenergie zwischen Pd und der SrTiO3(001)-Oberfläche zu bestimmt werden. Unter Verwendung der Ratentheorie konnte der Anfangszustand des Wachstums der Pd-Filme durch grundlegende Prozesse, wie die Diffusion, die Adsorption und die Keimbildung beschrieben werden. Aus dem Vergleich von experimentell gewonnenen maximalen Inseldichten mit der Ratentheorie konnte die kritische Keimgröße, die Diffusionsenergie, die Adsorptionsenergie und das Verhältnis von Diffusionskonstante zu Schwingungsfrequenz angegebenen werden. Neben der Keimbildung ließ sich in dieser Arbeit auch das Spätstadium der Koaleszenz studieren. Über Anwendung eines Modells von Jeffers gelang es, den Vorfaktor der Pd-Selbstdiffusion zu bestimmen. Aufgrund des Inselwachstums war es unmöglich, dünne epitaktische Filme, die das SrTiO3(001)-Substrat vollständig bedeckten, in einem einzigen Aufdampfschritt abzuscheiden. Durch einen kombinierten Prozeß aus verschiedenen Aufdampfschritten und anschließender Auslagerung gelang es jedoch sehr dünne geschlossene epitaktische Filme herzustellen. Dieser Prozeß basiert auf dem abnormalen Kornwachstum epitaktischer Körner.
Open Access
A complementary experimental and theoretical approach for probing the surface functionalization of ZnO with molecular catalyst linkers
(2023) Kousik, Shravan R.; Solodenko, Helena; YazdanYar, Azade; Kirchhof, Manuel; Schützendübe, Peter; Richter, Gunther; Laschat, Sabine; Fyta, Maria; Schmitz, Guido; Bill, Joachim; Atanasova, Petia
The application of ZnO materials as solid-state supports for molecular heterogeneous catalysis is contingent on the functionalization of the ZnO surface with stable self-assembled monolayers (SAMs) of catalyst linker molecules. Herein, experimental and theoretical methods are used to study SAMs of azide-terminated molecular catalyst linkers with two different anchor groups (silane and thiol) on poly and monocrystalline (0001, ) ZnO surfaces. Angle-resolved and temperature-dependent X-ray photoelectron spectroscopy (XPS) is used to study SAM binding modes, thermal stabilities, and coverages. The binding strengths and atomistic ordering of the SAMs are determined via atom-probe tomography (APT). Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations provide insights on the influence of the ZnO surface polarity on the interaction affinity and conformational behavior of the SAMs. The investigations show that SAMs based on 3-azidopropyltriethoxysilane possess a higher binding strength and thermal stability than the corresponding thiol. SAM surface coverage is strongly influenced by the surface polarity of ZnO, and the highest coverage is observed on the polycrystalline surface. To demonstrate the applicability of linker-modified polycrystalline ZnO as a catalyst support, a chiral Rh diene complex is immobilized on the azide-terminal of the SAM and its coverage is evaluated via XPS.
Open Access
Immune cell‐based microrobots for remote magnetic actuation, antitumor activity, and medical imaging
(2024) Dogan, Nihal Olcay; Suadiye, Eylül; Wrede, Paul; Lazovic, Jelena; Dayan, Cem Balda; Soon, Ren Hao; Aghakhani, Amirreza; Richter, Gunther; Sitti, Metin
Translating medical microrobots into clinics requires tracking, localization, and performing assigned medical tasks at target locations, which can only happen when appropriate design, actuation mechanisms, and medical imaging systems are integrated into a single microrobot. Despite this, these parameters are not fully considered when designing macrophage‐based microrobots. This study presents living macrophage‐based microrobots that combine macrophages with magnetic Janus particles coated with FePt nanofilm for magnetic steering and medical imaging and bacterial lipopolysaccharides for stimulating macrophages in a tumor‐killing state. The macrophage‐based microrobots combine wireless magnetic actuation, tracking with medical imaging techniques, and antitumor abilities. These microrobots are imaged under magnetic resonance imaging and optoacoustic imaging in soft‐tissue‐mimicking phantoms and ex vivo conditions. Magnetic actuation and real‐time imaging of microrobots are demonstrated under static and physiologically relevant flow conditions using optoacoustic imaging. Further, macrophage‐based microrobots are magnetically steered toward urinary bladder tumor spheroids and imaged with a handheld optoacoustic device, where the microrobots significantly reduce the viability of tumor spheroids. The proposed approach demonstrates the proof‐of‐concept feasibility of integrating macrophage‐based microrobots into clinic imaging modalities for cancer targeting and intervention, and can also be implemented for various other medical applications.
Open Access
Nanoscale mapping of magnetic auto-oscillations with a single spin sensor
(2025) Hache, Toni; Anshu, Anshu; Shalomayeva, Tetyana; Richter, Gunther; Stöhr, Rainer; Kern, Klaus; Wrachtrup, Jörg; Singha, Aparajita
Spin Hall nano-oscillators convert DC to magnetic auto-oscillations in the microwave regime. Current research on these devices is dedicated to creating next-generation energy-efficient hardware for communication technologies. Despite intensive research on magnetic auto-oscillations within the past decade, the nanoscale mapping of those dynamics remained a challenge. We image the distribution of free-running magnetic auto-oscillations by driving the electron spin resonance transition of a single spin quantum sensor, enabling fast acquisition (100 ms/pixel). With quantitative magnetometry, we experimentally demonstrate for the first time that the auto-oscillation spots are localized at magnetic field minima acting as local potential wells for confining spin-waves. By comparing the magnitudes of the magnetic stray field at these spots, we decipher the different frequencies of the auto-oscillation modes. The insights gained regarding the interaction between auto-oscillation modes and spin-wave potential wells enable advanced engineering of real devices.