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- ItemStabilizing a three-center single-electron metal–metal bond in a fullerene cage(Cambridge : RSC, 2021) Jin, Fei; Xin, Jinpeng; Guan, Runnan; Xie, Xiao-Ming; Chen, Muqing; Zhang, Qianyan; Popov, Alexey A.; Xie, Su-Yuan; Yang, ShangfengTrimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M3C2 cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy3C2@Ih(7)-C80 determined by single crystal X-ray diffraction shows that the encapsulated Dy3C2 cluster adopts a bat ray configuration, in which the acetylide unit C2 is elevated above the Dy3 plane by ∼1.66 Å, while Dy–Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy3)8+(C2)2−@C806− and features an unprecedented three-center single-electron Dy–Dy–Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc3C2@Ih(7)-C80 with a (Sc3)9+(C2)3−@C806− charge distribution and no metal–metal bonding.
- ItemHigh temperature behavior of rual thin films on piezoelectric CTGS and LGS substrates(Basel : MDPI AG, 2020) Seifert, M.This paper reports on a significant further improvement of the high temperature stability of RuAl thin films (110 nm) on the piezoelectric Ca3TaGa3Si2O14 (CTGS) and La3Ga5SiO14 (LGS) substrates. RuAl thin films with AlN or SiO2 cover layers and barriers to the substrate (each 20 nm), as well as a combination of both were prepared on thermally oxidized Si substrates, which serve as a reference for fundamental studies, and the piezoelectric CTGS, as well as LGS substrates. In somefilms, additional Al layers were added. To study their high temperature stability, the samples were annealed in air and in high vacuum up to 900 °C, and subsequently their cross-sections, phase formation, film chemistry, and electrical resistivity were analyzed. It was shown that on thermally oxidized Si substrates, all films were stable after annealing in air up to 800 °C and in high vacuum up to 900 °C. The high temperature stability of RuAl thin films on CTGS substrates was improved up to 900 °C in high vacuum by the application of a combined AlN/SiO2 barrier layer and up to 800 °C in air using a SiO2 barrier. On LGS, the films were only stable up to 600 °C in air; however, a single SiO2 barrier layer was sufficient to prevent oxidation during annealing at 900 °C in high vacuum.
- ItemPhase formation and high-temperature stability of very thin co-sputtered Ti-Al and multilayered Ti/Al films on thermally oxidized si substrates(Basel : MDPI AG, 2020) Seifert, M.; Lattner, E.; Menzel, S.B.; Oswald, S.; Gemming, T.Ti-Al thin films with a thickness of 200 nm were prepared either by co-sputtering from elemental Ti and Al targets or as Ti/Al multilayers with 10 and 20 nm individual layer thickness on thermally oxidized Si substrates. Some of the films were covered with a 20-nm-thick SiO2 layer, which was used as an oxidation protection against the ambient atmosphere. The films were annealed at up to 800 °C in high vacuum for 10 h, and the phase formation as well as the film architecture was analyzed by X-ray diffraction, cross section, and transmission electron microscopy, as well as Auger electron and X-ray photoelectron spectroscopy. The results reveal that the co-sputtered films remained amorphous after annealing at 600 °C independent on the presence of the SiO2 cover layer. In contrast to this, the γ-TiAl phase was formed in the multilayer films at this temperature. After annealing at 800 °C, all films were degraded completely despite the presence of the cover layer. In addition, a strong chemical reaction between the Ti and SiO2 of the cover layer and the substrate took place, resulting in the formation of Ti silicide. In the multilayer samples, this reaction already started at 600 °C.
- ItemSpin pumping at interfaces with ferro- and paramagnetic Fe60Al40films acting as spin source and spin sink(Melville, NY : American Inst. of Physics, 2022) Strusch, T.; Lenz, K.; Meckenstock, R.; Bali, R.; Ehrler, J.; Lindner, J.; Fassbender, J.; Farle, M.; Potzger, K.; Semisalova, A.We present a study of spin pumping efficiency and determine the spin mixing conductance and spin diffusion length in thin bilayer films based on 3d transition metal alloy Fe60Al40. Due to its magnetostructural phase transition, Fe60Al40 can be utilized as a ferromagnetic (FM) or paramagnetic (PM) material at the same temperature depending on its structural order; thus a thin Fe60Al40 film can act as a spin source or a spin sink when interfaced with a paramagnet or a ferromagnet, respectively. Ferromagnetic resonance measurements were performed in a frequency range of 5-35 GHz on bilayer films composed of FM-Fe60Al40/Pd and PM-Fe60Al40/Ni80Fe20 (permalloy). The increase in damping with the thickness of the paramagnetic layer was interpreted as a result of spin pumping into the paramagnet. We determine the spin mixing conductance g P d ↑↓ = (3.8 ± 0.5) × 10 18 m - 2 at the FM-Fe60Al40/Pd interface and the spin diffusion length λ P d = 9.1 ± 2.0 nm in Pd. For the PM-Fe60Al40/permalloy interface, we find a spin mixing conductance g F e A l ↑↓ = (2.1 ± 0.2) × 10 18 m - 2 and a spin diffusion length λ F e A l = 11.9 ± 0.2 nm for PM-Fe60Al40. The demonstrated bi-functionality of the Fe60Al40 alloy in spin pumping structures may be promising for spintronic applications.
- ItemTiNb2O7 and VNB9O25 of ReO3 type in hybrid Mg−Li batteries: Electrochemical and interfacial insights(Washington, DC : American Chemical Society, 2020) Maletti, Sebastian; Herzog-Arbeitman, Abraham; Oswald, Steffen; Senyshyn, Anatoliy; Giebeler, Lars; Mikhailova, DariaAs one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid-state synthesis and, for the first time, comprehensively examined in hybrid Mg−Li batteries. Both materials adopt ReO3-related structures differing in the interconnection of oxygen polyhedra and the resulting guest ion diffusion paths. We show applicability of the compounds in hybrid cells providing capacities comparable to those reached in Li-ion batteries (LIBs) at room temperature (220 mAh g−1 for TNO and 150 mAh g−1 for VNO, both at 0.1 C), their operability in the temperature range between −10 and 60 °C, and even better capacity retention than in pure LIBs, rendering this hybrid technology superior for long-term application. Post mortem X-ray photoelectron spectroscopy reveals a cathode−electrolyte interface as a key ingredient for providing excellent electrochemical stability of the hybrid battery. A significant contribution of the intercalation pseudocapacitance to charge storage was observed for both materials in Li- and Mg−Li batteries. However, the pseudocapacitive part is higher for TNO than for VNO, which correlates with structural distinctions, providing better accessibility of diffusion pathways for guest cations in TNO and, as a consequence, a higher ionic transport within the crystal structure. © 2020 American Chemical Society
- ItemStabilization of the ζ-Cu10Sn3 Phase by Ni at Soldering-Relevant Temperatures(Heidelberg : Springer Verlag, 2020) Wieser, C.; Hügel, W.; Martin, S.; Freudenberger, J.; Leineweber, A.A current issue in electrical engineering is the enhancement of the quality of solder joints. This is mainly associated with the ongoing electrification of transportation as well as the miniaturization of (power) electronics. For the reliability of solder joints, intermetallic phases in the microstructure of the solder are of great importance. The formation of the intermetallic phases in the Cu-Sn solder system was investigated for different annealing temperatures between 472 K and 623 K using pure Cu as well as Cu-1at.%Ni and Cu-3at.%Ni substrate materials. These are relevant for lead frame materials in electronic components. The Cu and Cu-Ni alloys were in contact to galvanic plated Sn. This work is focused on the unexpected formation of the hexagonal ζ-(Cu,Ni)10Sn3 phase at annealing temperatures of 523–623 K, which is far below the eutectoid decomposition temperature of binary ζ-Cu10Sn3 of about 855 K. By using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction the presence of the ζ phase was confirmed and its structural properties were analyzed.
- ItemInfluence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds(Cambridge : RSC Publ., 2020) Fernandez, L.; Blanco-Rey, M.; Castrillo-Bodero, R.; Ilyn, M.; Ali, K.; Turco, E.; Corso, M.; Ormaza, M.; Gargiani, P.; Valbuena, M.A.; Mugarza, A.; Moras, P.; Sheverdyaeva, P.M.; Kundu, Asish K.; Jugovac, M.; Laubschat, C.; Ortega, J.E.; Schiller, F.One-atom-thick rare-earth/noble metal (RE-NM) compounds are attractive materials to investigate two-dimensional magnetism, since they are easy to synthesize into a common RE-NM2 structure with high crystal perfection. Here we perform a comparative study of the GdAu2, HoAu2, and YbAu2 monolayer compounds grown on Au(111). We find the same atomic lattice quality and moiré superlattice periodicity in the three cases, but different electronic properties and magnetism. The YbAu2 monolayer reveals the characteristic electronic signatures of a mixed-valence configuration in the Yb atom. In contrast, GdAu2 and HoAu2 show the trivalent character of the rare-earth and ferromagnetic transitions below 22 K. Yet, the GdAu2 monolayer has an in-plane magnetic easy-axis, versus the out-of-plane one in HoAu2. The electronic bands of the two trivalent compounds are very similar, while the divalent YbAu2 monolayer exhibits different band features. In the latter, a strong 4f-5d hybridization is manifested in neatly resolved avoided crossings near the Fermi level. First principles theory points to a residual presence of empty 4f states, explaining the fluctuating valence of Yb in the YbAu2 monolayer. © The Royal Society of Chemistry.
- ItemRIXS interferometry and the role of disorder in the quantum magnet Ba3 Ti3-x Irx O9(College Park, MD : APS, 2023) Magnaterra, M.; Moretti Sala, M.; Monaco, G.; Becker, P.; Hermanns, M.; Warzanowski, P.; Lorenz, T.; Khomskii, D. I.; van Loosdrecht, P. H. M.; van den Brink, J.; Grüninger, M.Motivated by several claims of spin-orbit-driven spin-liquid physics in hexagonal Ba3Ti3-xIrxO9 hosting Ir2O9 dimers, we report on resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge for different x. We demonstrate that magnetism in Ba3Ti3-xIrxO9 is governed by an unconventional realization of strong disorder, where cation disorder affects the character of the local moments. RIXS interferometry, studying the RIXS intensity over a broad range of transferred momentum q, is ideally suited to assign different excitations to different Ir sites. We find pronounced Ir-Ti site mixing. Both ions are distributed over two crystallographically inequivalent sites, giving rise to a coexistence of quasimolecular singlet states on Ir2O9 dimers and spin-orbit-entangled j=1/2 moments of 5d5Ir4+ ions. RIXS reveals different kinds of strong magnetic couplings for different bonding geometries, highlighting the role of cation disorder for the suppression of long-range magnetic order in this family of compounds.
- ItemSelf-sufficient self-oscillating microsystem driven by low power at low Reynolds numbers(Washington, DC [u.a.] : American Association for the Advancement of Science, 2021) Akbar, Farzin; Rivkin, Boris; Aziz, Azaam; Becker, Christian; Karnaushenko, Dmitriy D.; Medina-Sánchez, Mariana; Karnaushenko, Daniil; Schmidt, Oliver G.Oscillations at several hertz are a key feature of dynamic behavior of various biological entities, such as the pulsating heart, firing neurons, or the sperm-beating flagellum. Inspired by nature’s fundamental self-oscillations, we use electroactive polymer microactuators and three-dimensional microswitches to create a synthetic electromechanical parametric relaxation oscillator (EMPRO) that relies on the shape change of micropatterned polypyrrole and generates a rhythmic motion at biologically relevant stroke frequencies of up to ~95 Hz. We incorporate an Ag-Mg electrochemical battery into the EMPRO for autonomous operation in a nontoxic environment. Such a self-sufficient self-oscillating microsystem offers new opportunities for artificial life at low Reynolds numbers by, for instance, mimicking and replacing nature’s propulsion and pumping units.