| 1. |
- Bainsla, Lakhan, et al.
(författare)
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Ultrathin Ferrimagnetic GdFeCo Films with Low Damping
- 2022
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 32:23, s. 2111693-
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic materials dominate as the magnetically active element in spintronic devices, but come with drawbacks such as large stray fields and low operational frequencies. Compensated ferrimagnets provide an alternative as they combine the ultrafast magnetization dynamics of antiferromagnets with a ferromagnet-like spin-orbit-torque behavior. However, to use ferrimagnets in spintronic devices their advantageous properties must be retained also in ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1−x thin films in the thickness range t = 2–20 nm are grown on high resistance Si(100) substrates and studied using broadband ferromagnetic resonance measurements at room temperature. By tuning their stoichiometry, a nearly compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1−x ultrathin films for the first time, with an effective magnetization of (Formula presented.) = 0.02 T and a low effective Gilbert damping constant of α = 0.0078, comparable to the lowest values reported so far in 30 nm films. These results show great promise for the development of ultrafast and energy efficient ferrimagnetic spintronic devices.
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| 2. |
- Wang, Chunlei, et al.
(författare)
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Inverse single-site Fe1(OH)X/Pt(111) model catalyst for preferential oxidation of CO in H2
- 2022
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Ingår i: Nano Reseach. - : Springer Nature. - 1998-0124 .- 1998-0000. ; 15:1, s. 709-715
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Tidskriftsartikel (refereegranskat)abstract
- Inverse oxide/metal model systems are frequently used to investigate catalytic structure-function relationships at an atomic level. By means of a novel atomic layer deposition process, growth of single-site Fe1Ox on a Pt(111) single crystal surface was achieved, as confirmed by scanning tunneling microscopy (STM). The redox properties of the catalyst were characterized by synchrotron radiation based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). After calcination treatment at 373 K in 1 mbar O2 the chemical state of the catalyst was determined as Fe3+. Reduction in 1 mbar H2 at 373 K demonstrates a facile reduction to Fe2+ and complete hydroxylation at significantly lower temperatures than what has been reported for iron oxide nanoparticles. At reaction conditions relevant for preferential oxidation of CO in H2 (PROX), the catalyst exhibits a Fe3+ state (ferric hydroxide) at 298 K while re-oxidation of iron oxide clusters does not occur under the same condition. CO oxidation proceeds on the single-site Fe1(OH)3 through a mechanism including the loss of hydroxyl groups in the temperature range of 373 to 473 K, but no reaction is observed on iron oxide clusters. The results highlight the high flexibility of the single iron atom catalyst in switching oxidation states, not observed for iron oxide nanoparticles under similar reaction conditions, which may indicate a higher intrinsic activity of such single interfacial sites than the conventional metal-oxide interfaces. In summary, our findings of the redox properties on inverse single-site iron oxide model catalyst may provide new insights into applied Fe-Pt catalysis. [Figure not available: see fulltext.]
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| 3. |
- Wang, Chunlei, et al.
(författare)
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Stabilization of Cu2O through Site-Selective Formation of a Co1Cu Hybrid Single-Atom Catalyst
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:5, s. 2313-2320
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Tidskriftsartikel (refereegranskat)abstract
- Single-atom catalysts (SACs) consist of a low coverage of isolated metal atoms dispersed on a metal substrate, called single-atom alloys (SAAs), or alternatively single metal atoms coordinated to oxygen atoms on an oxide support. We present the synthesis of a new type of Co1Cu SAC centers on a Cu2O(111) support by means of a site-selective atomic layer deposition technique. Isolated metallic Co atoms selectively coordinate to the native oxygen vacancy sites (Cu sites) of the reconstructed Cu2O(111) surface, forming a Co1Cu SAA with no direct Co- Ox bonds. The centers, here referred to as Co1Cu hybrid SACs, are found to stabilize the active Cu+ sites of the low-cost Cu2O catalyst that otherwise is prone to deactivation under reaction conditions. The stability of the Cu2O(111) surface was investigated by synchrotron radiation-based ambient-pressure X-ray photoelectron spectroscopy under reducing CO environment. The structure and reduction reaction are modeled by density functional theory calculations, in good agreement with experimental results.
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| 4. |
- Yu, H., et al.
(författare)
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Precise Construction of High Metallicity and High Stability TM1/Cu2O(111) Single-Atom Catalysts by First-Principles
- 2022
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Ingår i: Catalysis Letters. - : Springer Nature. - 1011-372X .- 1572-879X.
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Tidskriftsartikel (refereegranskat)abstract
- Single-atom catalysts (SACs) have attracted great interest in heterogeneous catalysis because of their excellent catalytic performance and suitable stability. Here, we construct a series of SACs by locating transition metal (TM) atoms on Cu2O(111) using first-principles. Due to the mightily change of the electronic and geometric properties, TM1/Cu2O(111) not only has good stability (binding energy less than − 2 eV), but also the catalyst, like alloys, retains the metallicity of single atoms to the greatest extent. Furthermore, the SACs TM1/Cu2O(111) reduce the band gap and promote charge transfer and charge separation. Pd1/Cu2O(111) exhibits excellent dual-effect catalytic capacity (overpotential of 1.23 V), with oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) barriers of 0.353 eV and 0.662 eV respectively. In the N2 reduction reaction (NRR), Mo1/Cu2O(111) performs the best. The distal mechanism is the most suitable reaction path in the catalytic reaction, and the free energy barrier of the rate-determining step is 0.464 eV. Our results provide a reference for the anchoring of TM in Cu2O(111), which facilitates the precise design of novel SACs. Graphical Abstract: [Figure not available: see fulltext.] The highly metallic and highly stable TM1/Cu2O(111) single-atom catalysts showexcellent performance in OER/ORR and NRR.
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