70 research outputs found
AgO investigated by photoelectron spectroscopy : Evidence for mixed valence
We present photoelectron spectroscopy investigations of in-situ prepared AgO. The sample was prepared by room temperature oxidation of Ag in an electron cyclotron resonance O2 plasma. In contrast to other measurements based on ex situ prepared AgO powder samples, our investigations show a distinct double peak structure of the O 1s signal with a remarkable chemical shift of 2.9 eV between the two O 1s components. These two components can not be motivated from a crystallographic point of view as the oxygen sites are all equivalent in the unit cell. We interpret this double peak structure as a characteristic feature of AgO and discuss it in terms of mixed valences
Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy
Atomically precise armchair graphene nanoribbons of width (7-AGNRs) are
investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis
of energy-dependent standing wave patterns of finite length ribbons allows, by
Fourier transformation, the direct extraction of the dispersion relation of
frontier electronic states. Aided by density functional theory calculations, we
assign the states to the valence band, the conduction band and the next empty
band of 7-AGNRs, determine effective masses of , and , respectively, and a band gap of eV.Comment: 20 pages, 7 figure
Coupled spin states in armchair graphene nanoribbons with asymmetric zigzag edge extensions
Carbon-based magnetic structures promise significantly longer coherence times
than traditional magnetic materials, which is of fundamental importance for
spintronic applications. An elegant way of achieving carbon-based magnetic
moments is the design of graphene nanostructures with an imbalanced occupation
of the two sublattices forming the carbon honeycomb lattice. According to
Lieb's theorem, this induces local magnetic moments that are proportional to
the sublattice imbalance. Exact positioning of sublattice imbalanced
nanostructures in graphene nanomaterials hence offers a route to control
interactions between induced local magnetic moments and to obtain graphene
nanomaterials with magnetically non-trivial ground states. Here, we show that
such sublattice imbalanced nanostructures can be incorporated along a large
band gap armchair graphene nanoribbon on the basis of asymmetric zigzag edge
extensions, which is achieved by incorporating specifically designed precursor
monomers during the bottom-up fabrication of the graphene nanoribbons. Scanning
tunneling spectroscopy of an isolated and electronically decoupled zigzag edge
extension reveals Hubbard-split states in accordance with theoretical
predictions. Investigation of pairs of such zigzag edge extensions reveals
ferromagnetic, antiferromagnetic or quenching of the magnetic interactions
depending on the relative alignment of the asymmetric edge extensions.
Moreover, a ferromagnetic spin chain is demonstrated for a periodic pattern of
zigzag edge extensions along the nanoribbon axis. This work opens a route
towards the design and fabrication of graphene nanoribbon-based spin chains
with complex magnetic ground states
Highly Enantioselective Adsorption of Small Prochiral Molecules on a Chiral Intermetallic Compound
Intrinsically chiral surfaces of intermetallic compounds are shown to be novel materials for enantioselective processes. Their advantage is the significantly higher thermal and chemical stability, and therefore their extended application range for catalyzed chiral reactions compared to surfaces templated with chiral molecular modifiers or auxiliaries. On the Pd-1-terminated PdGa(111) surface, room-temperature adsorption of a small prochiral molecule (9-ethynylphenanthrene) leads to exceptionally high enantiomeric excess ratios of up to 98%. Our findings highlight the great potential of intrinsically chiral intermetallic compounds for the development of novel, enantioselective catalysts that can be operated at high temperatures and potentially also in harsh chemical environments
On-surface synthesis of super-heptazethrene
Zethrenes are model diradicaloids with potential applications in spintronics and optoelectronics. Despite a rich chemistry in solution, on-surface synthesis of zethrenes has never been demonstrated. We report the on-surface synthesis of super-heptazethrene on Au(111). Scanning tunneling spectroscopy investigations reveal that super-heptazethrene exhibits an exceedingly low HOMOâLUMO gap of 230 meV and, in contrast to its open-shell singlet ground state in the solution phase and in the solid-state, likely adopts a closed-shell ground state on Au(111)
On-surface Synthesis of Edge-Extended Zigzag Graphene Nanoribbons.
Graphene nanoribbons (GNRs) have gained significant attention in nanoelectronics due to their potential for precise tuning of electronic properties through variations in edge structure and ribbon width. However, the synthesis of GNRs with highly sought-after zigzag edges (ZGNRs), critical for spintronics and quantum information technologies, remains challenging. In this study, we present a design motif for synthesizing a novel class of GNRs termed edge-extended ZGNRs. This motif enables the controlled incorporation of edge extensions along the zigzag edges at regular intervals. We successfully demonstrate the synthesis of a specific GNR instance-a 3-zigzag-rows-wide ZGNR-with bisanthene units fused to the zigzag edges on alternating sides of the ribbon axis. The resulting edge-extended 3-ZGNR is comprehensively characterized for its chemical structure and electronic properties using scanning probe techniques, complemented by density functional theory calculations. The design motif showcased here opens up new possibilities for synthesizing a diverse range of edge-extended ZGNRs, expanding the structural landscape of GNRs and facilitating the exploration of their structure-dependent electronic properties. This article is protected by copyright. All rights reserved
Collective AllâCarbon Magnetism in Triangulene Dimers
Triangular zigzag nanographenes, such as triangulene and its Ïâextended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for highâspin networks with longârange magnetic order, which are of immense fundamental and technological relevance. As a first step towards these lines, we present the onâsurface synthesis and a proofâofâprinciple experimental study of magnetism in covalently bonded triangulene dimers. Onâsurface reactions of rationally designed precursor molecules on Au(111) lead to the selective formation of triangulene dimers in which the triangulene units are either directly connected through their minority sublattice atoms, or are separated via a 1,4âphenylene spacer. The chemical structures of the dimers have been characterized by bondâresolved scanning tunneling microscopy. Scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy measurements reveal collective singletâtriplet spin excitations in the dimers, demonstrating efficient intertriangulene magnetic coupling.This work was supported by the Swiss National Science Foundation (grant numbers 200020-182015 and IZLCZ2-170184), the NCCR MARVEL funded by the Swiss National Science Foundation (grant number 51NF40-182892), the European Unionâs Horizon 2020 research and innovation program (grant number 785219, Graphene Flagship Core 2), the Office of Naval Research (grant number N00014-18-1-2708), an ERC Consolidator grant (T2DCP, grant number 819698), the German Research Foundation (DFG) within the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) and EnhanceNano (grant number 391979941), the European Social Fund and the Federal State of Saxony (ESF-Project GRAPHD, TU Dresden), the Generalitat Valenciana and Fondo Social Europeo (grant number ACIF/2018/175), MINECO-Spain (grant number MAT2016-78625), and the Portuguese FCT (grant number UTAPEXPL/NTec/0046/2017)
Collective AllâCarbon Magnetism in Triangulene Dimers
Triangular zigzag nanographenes, such as triangulene and its Ïâextended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for highâspin networks with longârange magnetic order, which are of immense fundamental and technological relevance. As a first step towards these lines, we present the onâsurface synthesis and a proofâofâprinciple experimental study of magnetism in covalently bonded triangulene dimers. Onâsurface reactions of rationally designed precursor molecules on Au(111) lead to the selective formation of triangulene dimers in which the triangulene units are either directly connected through their minority sublattice atoms, or are separated via a 1,4âphenylene spacer. The chemical structures of the dimers have been characterized by bondâresolved scanning tunneling microscopy. Scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy measurements reveal collective singletâtriplet spin excitations in the dimers, demonstrating efficient intertriangulene magnetic coupling.This work was supported by the Swiss National Science Foundation (grant numbers 200020-182015 and IZLCZ2-170184), the NCCR MARVEL funded by the Swiss National Science Foundation (grant number 51NF40-182892), the European Unionâs Horizon 2020 research and innovation program (grant number 785219, Graphene Flagship Core 2), the Office of Naval Research (grant number N00014-18-1-2708), an ERC Consolidator grant (T2DCP, grant number 819698), the German Research Foundation (DFG) within the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) and EnhanceNano (grant number 391979941), the European Social Fund and the Federal State of Saxony (ESF-Project GRAPHD, TU Dresden), the Generalitat Valenciana and Fondo Social Europeo (grant number ACIF/2018/175), MINECO-Spain (grant number MAT2016-78625), and the Portuguese FCT (grant number UTAPEXPL/NTec/0046/2017)
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