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Sökning: WFRF:(Ali Khadiza 1989)

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1.
  • Blanco-Rey, M., et al. (författare)
  • The Role of Rare-Earth Atoms in the Anisotropy and Antiferromagnetic Exchange Coupling at a Hybrid Metal–Organic Interface
  • 2024
  • Ingår i: Small. - 1613-6810 .- 1613-6829. ; In Press
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal–organic interface, a key component of an organic spintronic device. It is shown that the incorporation of 4f RE atoms to hybrid metal–organic interfaces of CuPc/REAu2 type (RE = Gd, Ho) constitutes a feasible approach toward on-demand magnetic properties and functionalities. The GdAu2 and HoAu2 substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu2 surface promotes the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic exchange coupling at the interface, induced by the 3d–4f superexchange interaction between the unpaired 3d electron of CuPc and the 4f electrons of the RE atoms. It is shown that 4f RE atoms with unquenched quantum orbital momentum ((Formula presented.)), as it is the case of Ho, induce an anisotropic interfacial exchange coupling.
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2.
  • Castrillo-Bodero, R., et al. (författare)
  • Tuning the carrier injection barrier of hybrid metal–organic interfaces on rare earth-gold surface compounds
  • 2023
  • Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 15:8, s. 4090-4100
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic hybrid metal-organic interfaces possess a great potential in areas such as organic spintronics and quantum information processing. However, tuning their carrier injection barriers on-demand is fundamental for the implementation in technological devices. We have prepared hybrid metal-organic interfaces by the adsorption of copper phthalocyanine CuPc on REAu2 surfaces (RE = Gd, Ho and Yb) and studied their growth, electrostatics and electronic structure. CuPc exhibits a long-range commensurability and a vacuum level pinning of the molecular energy levels. We observe a significant effect of the RE valence of the substrate on the carrier injection barrier of the hybrid metal-organic interface. CuPc adsorbed on trivalent RE-based surfaces (HoAu2 and GdAu2) exhibits molecular level energies that may allow injection carriers significantly closer to an ambipolar injection behavior than in the divalent case (YbAu2).
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3.
  • Datta, Sawani, et al. (författare)
  • Anomalies in the Dirac bands in the proximity of correlated electrons
  • 2024
  • Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 16:29, s. 13861-13866
  • Tidskriftsartikel (refereegranskat)abstract
    • Dirac fermions, particles with zero rest mass, are observed in topological materials and are believed to play a key role in the exotic phenomena in fundamental science and the advancement of quantum technology. Most of the topological systems studied so far are weakly correlated systems and the study of their properties in the presence of electron correlation is an interesting emerging area of research, where the electron correlation is expected to enhance the effective mass of the particles. Here, we studied the properties of Dirac bands in a non-symmorphic layered Kondo lattice system, CeAgSb2, employing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations. In addition to the Dirac cones due to non-symmorphic symmetry, this material hosts Dirac fermions in the squarenet layer in the proximity of a strongly correlated Ce layer exhibiting Kondo behavior. Experimental results reveal crossings of the highly dispersive linear bands at the Brillouin zone boundary due to non-symmorphic symmetry. In addition, there are anisotropic Dirac cones constituted by the squarenet Sb 5p states forming a diamond-shaped nodal line. These Dirac bands are linear in a wide energy range with an unusually high slope. Interestingly, near the local Ce 4f bands, these bands exhibit a change in the slope akin to the formation of a ‘kink’ observed in other materials due to electron-phonon coupling. The emergence of such exotic properties in proximity to strongly correlated electronic states has significant implications in the study of complex quantum materials including unconventional superconductors.
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4.
  • Eremeev, S. V., et al. (författare)
  • Insight into the electronic structure of the centrosymmetric skyrmion magnet GdRu 2 Si 2
  • 2023
  • Ingår i: Nanoscale Advances. - 2516-0230. ; 5:23, s. 6678-6687
  • Tidskriftsartikel (refereegranskat)abstract
    • The discovery of a square magnetic-skyrmion lattice in GdRu2Si2, with the smallest so far found skyrmion size and without a geometrically frustrated lattice, has attracted significant attention. In this work, we present a comprehensive study of surface and bulk electronic structures of GdRu2Si2 by utilizing momentum-resolved photoemission (ARPES) measurements and first-principles calculations. We show how the electronic structure evolves during the antiferromagnetic transition when a peculiar helical order of 4f magnetic moments within the Gd layers sets in. A nice agreement of the ARPES-derived electronic structure with the calculated one has allowed us to characterize the features of the Fermi surface (FS), unveil the nested region along kz at the corner of the 3D FS, and reveal their orbital compositions. Our findings suggest that the Ruderman-Kittel-Kasuya-Yosida interaction plays a decisive role in stabilizing the spiral-like order of Gd 4f moments responsible for the skyrmion physics in GdRu2Si2. Our results provide a deeper understanding of electronic and magnetic properties of this material, which is crucial for predicting and developing novel skyrmion-based systems.
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5.
  • Garcia-Martinez, Fernando, et al. (författare)
  • Structure Matters: Asymmetric CO Oxidation at Rh Steps with Different Atomic Packing
  • 2022
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 144:33, s. 15363-15371
  • Tidskriftsartikel (refereegranskat)abstract
    • Curved crystals are a simple but powerful approach to bridge the gap between single crystal surfaces and nanoparticle catalysts, by allowing a rational assessment of the role of active step sites in gas-surface reactions. Using a curved Rh(111) crystal, here, we investigate the effect of A-type (square geometry) and B-type (triangular geometry) atomic packing of steps on the catalytic CO oxidation on Rh at millibar pressures. Imaging the crystal during reaction ignition with laser-induced CO2 fluorescence demonstrates a two-step process, where B-steps ignite at lower temperature than A-steps. Such fundamental dissimilarity is explained in ambient pressure X-ray photoemission (AP-XPS) experiments, which reveal partial CO desorption and oxygen buildup only at B-steps. AP-XPS also proves that A-B step asymmetries extend to the active stage: at A-steps, low-active O-Rh-O trilayers buildup immediately after ignition, while highly active chemisorbed O is the dominant species on B-type steps. We conclude that B-steps are more efficient than A-steps for the CO oxidation.
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6.
  • Inagaki, Shunsuke, et al. (författare)
  • Effects of adsorbed molecular ordering to the superconductivity of a two-dimensional atomic layer crystal
  • 2023
  • Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 7:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) adsorption on the physical properties of the two-dimensional (2D) atomic layer superconductor (ALSC) In/Si(111)-(7×3) has been studied by angle-resolved photoelectron spectroscopy, transport measurements, and scanning tunneling microscopy. Hole doping from the adsorbed molecules has been reported to increase the superconducting transition temperature Tc of this ALSC, and the molecular spin tends to decrease it. Owing to its large electron affinity and its nonexistent spin state, the adsorption of PTCDA was expected to increase Tc. However, the PTCDA adsorption dopes only a small number of holes in the In layers and causes a suppression of Tc with a sharp increase in the normal-state sheet resistance followed by an insulating transition. Taking the disordering of the arrangement of PTCDA into account, we conclude that the increase in resistance is due to the localization effect originating from the random potential that is induced by the disordered PTCDA molecules. The present result also indicates the importance of the crystallinity of a 2D molecular film adsorbed on ALSCs. 
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7.
  • Mende, Max, et al. (författare)
  • Strong Rashba Effect and Different f−d Hybridization Phenomena at the Surface of the Heavy-Fermion Superconductor CeIrIn 5
  • 2022
  • Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 8:3
  • Tidskriftsartikel (refereegranskat)abstract
    • New temperature scales and remarkable differences from bulk properties have increasingly placed the surfaces of strongly correlated f materials into the focus of research activities. Applying first-principles calculations and angle-resolved photoelectron spectroscopy measurements, a strong Rashba effect and spin-split surface states at the CeIn surface of the heavy-fermion superconductor CeIrIn5 are revealed. The unveiled 4f-derived electron landscape is remarkably distinct for surface and bulk Ce implying the existence of novel temperature scales near the surface region in this material. These results show that ab initio calculations can reliably predict the unusual electronic and spin structure of surfaces of strongly correlated 4f systems where Rashba spin-orbit-coupling phenomena emerge. It is suggested that the structural blocks of such materials can be combined with magnetically active layers for engineering of novel nanostructural objects with appropriate substrates where the diversity of f-driven properties can be applied for the development of novel functionalities.
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8.
  • Mohammed Idris Bakhit, Alaa, et al. (författare)
  • A ferromagnetic Eu-Pt surface compound grown below hexagonal boron nitride
  • 2023
  • Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 15:27, s. 11517-11528
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the fundamental applications for monolayer-thick 2D materials is their use as protective layers of metal surfaces and in situ intercalated reactive materials in ambient conditions. Here we investigate the structural, electronic, and magnetic properties, as well as the chemical stability in air of a very reactive metal, Europium, after intercalation between a hexagonal boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu intercalation leads to a hBN-covered ferromagnetic EuPt2 surface alloy with divalent Eu2+ atoms at the interface. We expose the system to ambient conditions and find a partial conservation of the di-valent signal and hence the Eu-Pt interface. The use of a curved Pt substrate allows us to explore the changes in the Eu valence state and the ambient pressure protection at different substrate planes. The interfacial EuPt2 surface alloy formation remains the same, but the resistance of the protecting hBN layer to ambient conditions is reduced, likely due to a rougher surface and a more discontinuous hBN coating.
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9.
  • Schiller, F., et al. (författare)
  • Near-Ambient Pressure Oxidation of Silver in the Presence of Steps: Electrophilic Oxygen and Sulfur Impurities
  • 2024
  • Ingår i: ACS Catalysis. - 2155-5435. ; , s. 12865-12874
  • Tidskriftsartikel (refereegranskat)abstract
    • The oxidation of Ag crystal surfaces has recently triggered strong controversies around the presence of sulfur impurities that may catalyze reactions, such as the alkene epoxidations, especially the ethylene epoxidation. A fundamental challenge to achieve a clear understanding is the variety of procedures and setups involved as well as the particular history of each sample. Especially, for the often-used X-ray photoemission technique, product detection, or photoemission peak position overlap are problematic. Here we investigate the oxidation of the Ag(111) surface and its vicinal crystal planes simultaneously, using a curved crystal sample and in situ X-ray photoelectron spectroscopy at 1 mbar O2 near-ambient pressure conditions to further investigate surface species. The curved geometry allows a straightforward comparative analysis of the surface oxidation kinetics at different crystal facets, so as to precisely correlate the evolution of different oxygen species, namely nucleophilic and electrophilic oxygen, and the buildup of sulfur as a function of the crystal orientation. We observed that emission from both surface and bulk oxide contributes to the characteristic nucleophilic oxygen core-level peak, which arises during oxygen dosing and rapidly saturates below temperatures of 180 °C. The electrophilic oxygen peak appears later, growing at a slower but constant rate, at the expenses of the surface oxide. Electrophilic oxygen and sulfur core-levels evolve in parallel in all crystal facets, although faster and stronger at vicinal surfaces featuring B-type steps with {111} microfacets. Our study confirms the intimate connection of the electrophilic species with the formation of adsorbed SO4, and points to a higher catalytic activity of B-type stepped silver surfaces for alkene epoxidation or methane to formaldehyde conversion.
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10.
  • Tarasov, Artem V., et al. (författare)
  • Structural instability at the In-terminated surface of the heavy-fermion superconductor CeIrIn5
  • 2022
  • Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Driven by reconstruction and relaxation, by the appearance of surface electron states and resonances, the surface properties and related temperature scales of strongly correlated f-materials may differ dramatically from those in the bulk. Applying low energy electron and photoelectron diffraction techniques, momentum-resolved photoelectron spectroscopy and ab initio calculations, we demonstrate that the In-terminated surface of the heavyfermion superconductor CeIrIn5 experiences a reconstruction with a (root 2v x root 2)R45 degrees ordered structure. The latter appears due to the displacement of In atoms with respect to the Ir sublattice. We show that the electronic structure and related properties of the reconstructed In surface differ remarkably from the unreconstructed case. Namely, the predicted surface states with Rashba-type spin splitting do not appear. Our results suggest surface instabilities in similar quasi-two-dimensional strongly correlated f-materials, for which surface reconstructions can be unveiled by means of diffraction techniques.
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  • Resultat 1-10 av 12
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