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- ItemBackside metallization affects residual stress and bending strength of the recast layer in laser-diced Si(Elsevier, 2024-10-01) Ziegelwanger, Tobias; Reisinger, Michael; Matoy, Kurt; Medjahed, Asma Aicha; Zálešák, Jakub; Gruber, Manuel; Meindlhumer, Michael; Keckes, JozefThin Silicon dies separated by laser dicing form a thin layer via redeposition of ablated silicon known as recast layer. This work analyzed the influence of the recast layer microstructure and nanoscale residual stress gradients on the bending strength of bare and metalized silicon dies <100 mu m. Scanning and transmission electron microscopy revealed an intricate microstructure of ablated silicon and elements of the wafer backside metallization within the recast layer. Refined silicon grains decorated by nanoscopic metallic precipitates at their grain boundaries were observed. Cross-sectional synchrotron X-ray nanodiffraction revealed that the altered microstructure increased the tensile residual stress from 200 to 295 MPa for bare and metalized dies, respectively. Additionally, the metalized die exhibited gradients in residual stress and grain size between the die front- and backside. Despite their similar frontside bending strengths of -340 MPa, observed in 3-point bending experiments, a considerable strengthening of the backside from 425 up to 957 MPa was measured for bare and metalized die, respectively. The origins of the tensile residual stress and the influence of the backside metallization on the die bending strength are discussed.
- ItemUnidirectional propagation of zero-momentum magnons(AIP Publishing, 2024-09-23) Wojewoda, Ondřej; Holobrádek, Jakub; Pavelka, Dominik; Pribytova, Ekaterina; Krčma, Jakub; Klíma, Jan; Panda, Jaganandha; Michalička, Jan; Lednický, Tomáš; Chumak, Andrii V.; Urbánek, MichalWe report on experimental observation of unidirectional propagation of zero-momentum magnons in synthetic antiferromagnet consisting of strained CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic antiferromagnets with uniaxial anisotropy results in smooth and monotonous dispersion relation around Gamma point, where the direction of the phase velocity is reversed, while the group velocity direction is conserved. The experimental observation of this phenomenon by intensity-, phase-, and time-resolved Brillouin light scattering microscopy is corroborated by analytical models and micromagnetic simulations.
- ItemTemperature Dependence of Relativistic Valence Band Splitting Induced by an Altermagnetic Phase Transition(WILEY-V C H VERLAG GMBH, 2024-08-01) Hajlaoui, Mahdi; Wilfred D'Souza, Sunil; Šmejkal, Libor; Kriegner, Dominik; Krizman, Gauthier; Zakusylo, Tetiana; Olszowska, Natalia; Caha, Ondřej; Michalička, Jan; Sánchez-Barriga, Jaime; Marmodoro, Alberto; Výborný, Karel; Ernst, Arthur; Cinchetti, Mirko; Minár, Ján; Jungwirth, Tomáš; Springholz, GuntherAltermagnetic (AM) materials exhibit non-relativistic, momentum-dependent spin-split states, ushering in new opportunities for spin electronic devices. While the characteristics of spin-splitting are documented within the framework of the non-relativistic spin group symmetry, there is limited exploration of the inclusion of relativistic symmetry and its impact on the emergence of a novel spin-splitting in the band structure. This study delves into the intricate relativistic electronic structure of an AM material, alpha-MnTe. Employing temperature-dependent angle-resolved photoelectron spectroscopy across the AM phase transition, the emergence of a relativistic valence band splitting concurrent with the establishment of magnetic order is elucidated. This discovery is validated through disordered local moment calculations, modeling the influence of magnetic order on the electronic structure and confirming the magnetic origin of the observed splitting. The temperature-dependent splitting is ascribed to the advent of relativistic spin-splitting resulting from the strengthening of AM order in alpha-MnTe as the temperature decreases. This sheds light on a previously unexplored facet of this intriguing material. Altermagnets exhibit momentum-dependent spin-split states providing new opportunities for spin electronic devices. Through temperature-dependent angle-resolved photoemission spectroscopy and disordered local moment calculations, it is demonstrated that the relativistic valence band splitting of the prototypical MnTe altermagnet is of magnetic origin. This is attributed to a novel relativistic spin-splitting phenomenon concurrent with the establishment of the altermagnetic order below the N & eacute;el temperature. image
- ItemTop-down Surfactant-Free Synthesis of Supported Palladium-Nanostructured Catalysts(WILEY, 2024-03-01) Schott, Christian M.; Schneider, Peter M.; Sadraoui, Kais; Song, Kun-Ting; Garlyyev, Batyr; Watzele, Sebastian; Michalička, Jan; Macák, Jan; Viola, Arnaud; Maillard, Frederic; Senyshyn, Anatoliy; Fischer, Johannes A.; Bandarenka, Aliaksandr S.; Gubanova, Elena L.Nanostructured palladium (Pd) is a universal catalyst that is widely used in applications ranging from catalytic converters of combustion engine cars to hydrogenation catalysts in industrial processes. Standard protocols for synthesizing such nanoparticles (NPs) typically use bottom-up approaches. They utilize special and often expensive physical techniques or wet-chemical methods requiring organic surfactants. These surfactants should often be removed before catalytic applications. In this article, the synthesis of Pd NPs immobilized on carbon support by electrochemical erosion without using any surfactants or toxic materials is reported. The Pd NPs synthesis essentially relies on a Pd bulk pretreatment, which causes material embrittlement and allows the erosion process to evolve more efficiently, producing homogeneously distributed NPs on the support. Moreover, the synthesized catalyst is tested for hydrogen evolution reaction. The activity evaluations identify optimal synthesis parameters related to the erosion procedure. The electrocatalytic properties of the Pd NPs produced with sizes down to 6.4 +/- 2.9 nm are compared with a commercially available Pd/C catalyst. The synthesized catalyst outperforms the commercial catalyst within all properties, like specific surface area, geometric activity, mass activity, specific activity, and durability. A surfactant-free top-down approach, called "electrochemical erosion", allows the fabrication of palladium (Pd) nanoparticles (NPs) supported on Vulcan carbon. Crucially, a Pd wire pretreatment is identified as the essential step to synthesize NPs with sizes below 10 nm. The synthesized Pd/C catalysts are thoroughly analyzed for their structure, morphology, chemical composition, and electrochemical activity toward the hydrogen evolution reactions.image (c) 2024 WILEY-VCH GmbH
- ItemTop-down surfactant-free electrosynthesis of magnéli phase Ti9O17 nanowires(Royal Society of Chemistry, 2024-03-18) Schneider, Peter M.; Schott, Christian M.; Maier, Dominic; Watzele, Sebastian; Michalička, Jan; Rodriguez Pereira, Jhonatan; Hromádko, Luděk; Macák, Jan; Baran, Volodymyr; Senyshyn, Anatoliy; Viola, Arnaud; Maillard, Frederic; Gubanova, Elena L.; Bandarenka, Aliaksandr S.TiO2 nanowires have proven their importance as a versatile material in numerous fields of technology due to their unique properties attributable to their high aspect ratio and large surface area. However, synthesis is an enormous challenge since state-of-the-art techniques rely on complex, multi-stage procedures with expensive, specialized equipment, employing high-temperature steps and potentially toxic precursor materials and surfactants. Hence, we elucidate a simple and facile top-down methodology for the synthesis of nanowires with non-stoichiometric Magn & eacute;li phase Ti9O17. This methodology relies on the electrochemical erosion of bulk Ti wires immersed in an aqueous electrolyte, circumventing the use of environmentally harmful precursors or surfactants, eliminating the need for high temperatures, and reducing synthesis complexity and time. Using multiple techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, we provide evidence of the successful synthesis of ultrathin nanowires with the crystal structure of non-stoichiometric Ti9O17 Magn & eacute;li phase. The nanowire width of similar to 5 nm and the Brunauer-Emmett-Teller surface area of similar to 215 m(2) g(-1) make the nanowires presented in this work comparable to those synthesized by state-of-the-art bottom-up techniques.