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- ItemTowards 3D determination of the surface roughness of core-shell microparticles as a routine quality control procedure by scanning electron microscopy(NATURE PORTFOLIO, 2024-08-02) Hülagü, Deniz; Tobias, Charlie; Dao, Radek; Komarov, Pavel; Rurack, Knut; Hodoroaba, VasileDanRecently, we have developed an algorithm to quantitatively evaluate the roughness of spherical microparticles using scanning electron microscopy (SEM) images. The algorithm calculates the root-mean-squared profile roughness (RMS-RQ) of a single particle by analyzing the particle's boundary. The information extracted from a single SEM image yields however only two-dimensional (2D) profile roughness data from the horizontal plane of a particle. The present study offers a practical procedure and the necessary software tools to gain quasi three-dimensional (3D) information from 2D particle contours recorded at different particle inclinations by tilting the sample (stage). This new approach was tested on a set of polystyrene core-iron oxide shell-silica shell particles as few micrometer-sized beads with different (tailored) surface roughness, providing the proof of principle that validates the applicability of the proposed method. SEM images of these particles were analyzed by the latest version of the developed algorithm, which allows to determine the analysis of particles in terms of roughness both within a batch and across the batches as a routine quality control procedure. A separate set of particles has been analyzed by atomic force microscopy (AFM) as a powerful complementary surface analysis technique integrated into SEM, and the roughness results have been compared.
- 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.
- ItemSynergistic effect of Pd single atoms and nanoparticles deposited on carbon supports by ALD boosts alkaline hydrogen evolution reaction(Elsevier, 2024-02-15) Bawab, Bilal; Thalluri, Sitaramanjaneya Mouli; Kolíbalová, Eva; Zazpe Mendioroz, Raúl; Jelínek, Luděk; Rodriguez Pereira, Jhonatan; Macák, JanThe synergistic effects between carbon supports and noble metal species of an electrocatalyst are known to effectively boost the alkaline hydrogen evolution reaction (HER). Herein, Atomic Layer Deposition (ALD) was employed to decorate carbon papers with Pd species comprising single atoms (SAs) and nanoparticles (NPs). Transmission electron microscopy analysis revealed the metallic nature and coexistence of Pd as SAs and NPs. The results of X-ray photoelectron spectroscopy supported the evidenced SA species, manifested as the Pd+2. An increase in the electrochemical active surface area from 12.98 to 413.48 cm -2 was evidenced with increasing ALD cycles from 30 to 300c Pd and remained unchanged until 600c Pd. The exceptional overpotential for CP 600c Pd exhibits the lowest value of 4.55 mV, compared to previous reports for Pd electrocatalysts in a nonacidic environment, and confirms the synergistic effect of Pd SAs and NPs that plays a major role in enhancing alkaline HER.