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X-Ray Magnetic Circular Dichroism of Dinuclear Cobalt Dyprosium Compounds
No full textX-ray magnetic circular dichroism (XMCD) has been applied to investigate the magnetic properties of CoII(btmp)2(µ-piv)DyIII(piv)2 and to probe how these properties are dependent on the interaction between the Co and Dy.
XMCD is an element specific measurement based on X-ray absorption spectroscopy (XAS), with the use of circularly polarised X-rays while an external magnetic field is applied to the sample. In an XAS experiment, an incident X-ray excites a core electron to the valence band; the energy of the incident X-ray is discrete and characteristic of the element and transition which the electron undertakes. In XMCD the absorption intensity is dependent on the availability of spin up and spin down holes in the valence band. Varying the direction of the external magnetic field or polarisation enables the production of difference spectra which are characteristic of the ground state magnetic structure [1].
Lanthanide single-molecule magnets (SMM) are an area of significant interest due to the improvements in slow relaxation of the magnetisation achieved thus far [2], and their potential for enhancing information storage density, enabling the production of smaller electronic devices. CoII(btmp)2(µ-piv)DyIII(piv)2 possesses properties of a SMM. Herein, Co has a coordination of 5 in a distorted square pyramid polyhedral and Dy is within a 9-fold coordinated muffin type polyhedral [3]. To elucidate the dependence of magnetic properties in this SMM on the interaction between Co and Dy, CoII(btmp)2(µ-piv)YIII(piv)2 and ZnII(btmp)2(µ-piv)DyIII(piv)2, molecules where Y and Zn have been substituted for Dy and Co respectively. Magnetic properties of all three molecules were characterised by classical magnetometry. For Co-Dy the magnetic susceptibility decreases from 250 K to a minimum at ca. 12.5 K, where a sharp change denotes a transition in magnetic behaviour.
XMCD experiments at the Co L2,3 and Dy M4,5¬ edges were performed on the three compounds described above to investigate the magnetic structures of Co and Dy. Data were collected under a magnetic field of + 1.8 T and -1.8 T and with parallel and antiparallel circularly polarised X-rays. Samples were prepared for measurement by grinding into powder and pressing into indium foil. Measurements were performed at Beamline 6.3.1. at the Advanced Light source, Lawrence Berkeley National Laboratory, USA. Initial observations indicate Co–Dy interactions evident in the room-temperature Co L2,3 XAS. These interactions will be discussed in light of Dy M4,5¬ edge XMCD at 25 and 10 K [4]
Die Zukunft der Antriebe – Wasserstoff, E-Fuels, Batterien? (Prof. Dr. Maximilian Fichtner)
No full textDer Chemiker und Sprecher des Exzellenzclusters „Post Lithium Storage“ (POLiS) Prof. Dr. Maximilian Fichtner geht in seinem Vortrag der Frage nach, welche neuen Antriebstechnologien im Hinblick auf die Endlichkeit der fossilen Ressourcen zukünftig eingesetzt werden können. Er beleuchtet dabei Vor- und Nachteile verschiedener Antriebstechnologien wie Verbrenner mit eFuels, Wasserstoffantriebe und batterieelektrische Antriebe.
Der Vortrag von Prof. Dr. Maximilian Fichtner fand am 18. Dezember 2025 am Karlsruher Institut für Technologie (KIT) statt. Er ist Teil der Vortragsreihe Colloquium Fundamentale mit dem Titel „Watt jetzt? Energiewende zwischen Technologie und Teilhabe“.
Weitere Informationen: https://www.forum.kit.edu/colloquium_fundamental
Technikanthropologie und "menschliche Natur". Folgenreflexion – Enhancement – Neuroethik
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Development of a Platform for Spatiotemporal Analysis of Microbial Communities in Model Ecosystems
No full textResidual stress in Germanium single crystals caused by femtosecond laser micromachining
No full textFemtosecond laser (fs-laser) milling has emerged as a promising technique for high-precision material processing, offering significantly faster ablation rates compared to Ga+ Focused Ion Beam (FIB) milling. While fs-laser ablation is often considered to be athermal, its impact on surface features, such as redeposited material, raises concerns about its influence on microstructure and residual stress fields. This study explores the mechanical effects of fs-laser and FIB milling on a germanium single crystal, using synchrotron-based Laue microdiffraction coupled with Digital Image Correlation to characterize induced residual stresses and their spatial distribution. The further development of this technique allows to push the strain resolution to 10⁻⁵, which enabled a clear identification of the influence of the redeposition structure
Results of the SPIZWURZ bundle test
No full textThe 21-rod SPIZWURZ test bundle with three types of unirradiated claddings (opt. ZIRLO, Zry-4, DX-D4) was used to conduct a long-term integral experiment, approximately simulating dry storage conditions. A variety of parameters typical of an integrated test allowed for the acquisition of a large amount of experimental data necessary for verifying the corresponding computer codes. The claddings were preliminarily hydrogenated to concentrations of 100 and 300 wppm in a specially designed HOKI tubular furnace, distributed as uniformly as possible over a 1.3 m length. Hydrogenation was carried out at 450 °C by sequentially feeding fixed masses of hydrogen through a specially treated inner surface of the claddings. It was noted that the rate of hydrogenation of the opt. ZIRLO claddings is 1.5 times lower than for the Zry-4 claddings. After the hydrogen loading of the cladding tubes, the axial distribution of hydrogen was determined by laser scanning profilometry calibrated by hot gas extraction.
During the experiment, two values of internal rod pressure were used: 106 and 146 bar, which were maintained constant throughout the experiment (250 days). The peak cladding temperature decreased in steps of ≈15 K from 400 to 165 °C (average cooling rate ≈0.9 K/day). The maximal cooling rate during each temperature step was 6 K/h, step duration was about 10 h.
The post-test laser scanner measurements of the outer cladding diameter showed significant creep: radial deformation values are between 0.2 and 3.3% (diameter increase and the corresponding wall thinning). The largest creep of 3.3% was measured for opt. ZIRLO claddings hydrogenated to 300 wppm. The corresponding maximum creep value was 0.93% for Zry-4 and 1% for DX-D4. A clearly visible dependence of the degree of creep on the hydrogen concentration is observed for the opt. ZIRLO claddings: the creep of claddings hydrogenated to 300 wppm is 1.2-1.5 times higher than that of claddings hydrogenated to 100 wppm. A number of claddings show radially asymmetric wall thinning, which can be associated with the radial shift of the pellets from the central axis of the rod and the corresponding asymmetric heat supply along the circumference of the cladding.
The metallographic investigations revealed a uniform distribution of hydrides throughout the entire cladding circumference for all three cladding types used. In the DX-D4 claddings, hydrogen primarily diffused toward the outer liner. The degree of hydride reorientation was significantly higher in the Zry-4 claddings compared to the opt. ZIRLO claddings.
The difference in the behavior of the Zry-4 and opt. ZIRLO may be due, in part, to their different grain microstructures. Opt. ZIRLO claddings have a finer grain size than Zry-4. Moreover, although the temperatures during hydrogenation (450 °C) and the experiment itself (max. 400 °C) were relatively low, EBSD measurements showed grain growth from approx. 6 μm for the initial state to post-test 16 μm for Zry-4 (12 μm after hydrogenation), and from initial 3 μm to post-test 4.3 μm for opt. ZIRLO
Ytterbium ions and color centers in silicon carbide as cavity-integrated quantum nodes with near-infrared optical transitions
No full textQuantentechnologien aller Art, wie Quantencomputer und Quantensensoren, entwickeln sich rasant fort. Daraus resultiert ein großes technologisches Bedürfnis, Quanteninformationen zwischen solchen lokalen Systemen über große Distanzen hinweg auszutauschen. Hierfür benötigt man effiziente Quanten-Netzwerkschnittstellen, die es erlauben Quanteninformationen auf Photonen zu übertragen. Optisch aktive Defektzentren und dotierte Ionen in Festkörpern sind ideale Kandidaten für solche Quanten-Netzwerkschnittstellen, da sie sowohl über einen langlebigen und kohärenten Spin-Freiheitsgrad, als auch kohärente optische Übergange verfügen. Um die optischen Übergänge effizient zu machen und auf diese Weise hohe Kommunikationsraten zu erzielen, müssen diese photonisch verstärkt werden. Dies kann durch die Kopplung an faserbasierte Fabry-Pérot Mikroresonatoren hoher Güte erzielt werden. Diese Arbeit untersucht die Eignung von Ytterbiumionen sowie Defektzentren in Siliziumkarbid als Quantennetzwerkschnittstellen in solch einer resonatorbasierten Geometrie. Zu Beginn werden Ytterbiumdotanden in nanoskaligen Kristallen spektroskopisch untersucht. Diese zeigen schmale Ensemble-Linienbreiten bei kryogenen Temperaturen. Mit Hilfe von Sättigungspektroskopie wurde zum ersten Mal für dieses Material eine Obergrenze für die optische Linienbreite eines einzelnen Ions von 5 MHz bestimmt. Zudem wurde gezeigt, dass sich diese Nanokristalle in einen faserbasierten Resonatoraufbau integrieren lassen, der optische Spektroskopie erlaubt.
Anschließend wurden die optischen Eigenschaften von Ytterbiumionen in verschiedenen organischen Molekülen charakterisiert. Diese unterscheiden sich teilweise deutlich voneinander. Durch einen systematischen Vergleich wurde versucht, diese Variationen durch die molekulare Struktur zu erklären. Insbesondere für die nichtradiative Zerfallsrate wurden dabei erste Korrelationen gefunden.
Schließlich wurden Experimente an Farbzentren in Siliziumkarbid in einem kryogenen Resonatorsystem durchgeführt. Dafür wurde eine wenige Mikrometer dicke Membran aus Siliziumkarbid in einen faserbasierten Hohlraumresonator integriert. Das Resonatorsystem wurde sorgfältig charakterisiert und für gut geeignet befunden, da nur minimale Verluste durch die Membran entstanden. Durch die hohe spektrale Selektivität des Resonator konnten die kohärenten Übergänge einzelner Farbzentren bei kryogenen Temperaturen aufgelöst werden, was durch Analyse der Photonenstatistik verifiziert wurde. Schließlich wurde die Purcell-Verstärkung anhand einer verstimmungsabhängigen Lebenszeitmessung bestimmt. Durch die Kopplung an den Resonator wird der kohärente Übergang eines einzelnen Farbzentrums bis zu 13-fach verstärkt, was zu einer hohen Rate an kohärenten Einzelphotonen führt