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Halle J, Néel N, Kröger J. Monolayer and Bilayer Graphene on Ru(0001): Layer-Specific and Moiré-Site-Dependent Phonon Excitations. J Phys Chem Lett 2021; 12:6889-6894. [PMID: 34279966 DOI: 10.1021/acs.jpclett.1c01802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Graphene phonons are excited by the local injection of electrons and holes from the tip of a scanning tunneling microscope. Despite the strong graphene-Ru(0001) hybridization, monolayer graphene unexpectedly exhibits pronounced phonon signatures in inelastic electron tunneling spectroscopy. Spatially resolved spectroscopy reveals that the strength of the phonon signal depends on the site of the moiré lattice with a substantial red-shift of phonon energies compared to those of free graphene. Bilayer graphene gives rise to more pronounced spectral signatures of vibrational quanta with energies nearly matching the free graphene phonon energies. Spectroscopy data of bilayer graphene indicate moreover the presence of a Dirac cone plasmon excitation.
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Affiliation(s)
- Johannes Halle
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
| | - Nicolas Néel
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
| | - Jörg Kröger
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
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Kastorp CFP, Duncan DA, Scheffler M, Thrower JD, Jørgensen AL, Hussain H, Lee TL, Hornekær L, Balog R. Growth and electronic properties of bi- and trilayer graphene on Ir(111). NANOSCALE 2020; 12:19776-19786. [PMID: 32966486 DOI: 10.1039/d0nr04788k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Interesting electronic properties arise in vertically stacked graphene sheets, some of which can be controlled by mutual orientation of the adjacent layers. In this study, we investigate the MBE grown multilayer graphene on Ir(111) by means of STM, LEED and XPS and we examine the influence of the substrate on the geometric and electronic properties of bilayer graphene by employing XSW and ARPES measurements. We find that the MBE method does not limit the growth to two graphene layers and that the wrinkles, which arise through extended carbon deposition, play a crucial role in the multilayer growth. We also find that the bilayer and trilayer graphene sheets have graphitic-like properties in terms of the separation between the two layers and their stacking. The presence of the iridium substrate imposes a periodic potential induced by the moiré pattern that was found to lead to the formation of replica bands and minigaps in bilayer graphene. From tight-binding fits to our ARPES data we find that band renormalization takes place in multilayer graphene due to a weaker coupling of the upper-most graphene layer to the iridium substrate.
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Affiliation(s)
- Claus F P Kastorp
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark.
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Halle J, Néel N, Kröger J. Tailoring Intercalant Assemblies at the Graphene-Metal Interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:2554-2560. [PMID: 30665296 DOI: 10.1021/acs.langmuir.8b03879] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The influence of graphene on the assembly of intercalated material is studied using low-temperature scanning tunneling microscopy. Intercalation of Pt under monolayer graphene on Pt(111) induces a substrate reconstruction that is qualitatively different from the lattice rearrangement induced by metal deposition on Pt(111) and, specifically, the homoepitaxy of Pt. Alkali metals Cs and Li are used as intercalants for monolayer and bilayer graphene on Ru(0001). Atomically resolved topographic data reveal that at elevated alkali metal coverage (2 × 2)Cs and (1 × 1)Li intercalant structures form with respect to the graphene lattice.
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Affiliation(s)
- Johannes Halle
- Institut für Physik , Technische Universität Ilmenau , D-98693 Ilmenau , Germany
| | - Nicolas Néel
- Institut für Physik , Technische Universität Ilmenau , D-98693 Ilmenau , Germany
| | - Jörg Kröger
- Institut für Physik , Technische Universität Ilmenau , D-98693 Ilmenau , Germany
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Simon S, Voloshina E, Tesch J, Förschner F, Enenkel V, Herbig C, Knispel T, Tries A, Kröger J, Dedkov Y, Fonin M. Layer-by-Layer Decoupling of Twisted Graphene Sheets Epitaxially Grown on a Metal Substrate. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1703701. [PMID: 29450969 DOI: 10.1002/smll.201703701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 12/23/2017] [Indexed: 06/08/2023]
Abstract
The electronic properties of graphene can be efficiently altered upon interaction with the underlying substrate resulting in a dramatic change of charge carrier behavior. Here, the evolution of the local electronic properties of epitaxial graphene on a metal upon the controlled formation of multilayers, which are produced by intercalation of atomic carbon in graphene/Ir(111), is investigated. Using scanning tunneling microscopy and Landau-level spectroscopy, it is shown that for a monolayer and bilayers with small-angle rotations, Landau levels are fully suppressed, indicating that the metal-graphene interaction is largely confined to the first graphene layer. Bilayers with large twist angles as well as twisted trilayers demonstrate a sequence of pronounced Landau levels characteristic for a free-standing graphene monolayer pointing toward an effective decoupling of the top layer from the metal substrate. These findings give evidence for the controlled preparation of epitaxial graphene multilayers with a different degree of decoupling, which represent an ideal platform for future electronic and spintronic applications.
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Affiliation(s)
- Sabina Simon
- Department of Physics, University of Konstanz, 78457, Konstanz, Germany
| | - Elena Voloshina
- Physics Department, Shanghai University, Shanghai, 200444, China
| | - Julia Tesch
- Department of Physics, University of Konstanz, 78457, Konstanz, Germany
| | - Felix Förschner
- Department of Physics, University of Konstanz, 78457, Konstanz, Germany
| | - Vivien Enenkel
- Department of Physics, University of Konstanz, 78457, Konstanz, Germany
| | - Charlotte Herbig
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937, Köln, Germany
- Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Timo Knispel
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937, Köln, Germany
| | - Alexander Tries
- Institut für Physik, Technische Universität Ilmenau, 98693, Ilmenau, Germany
| | - Jörg Kröger
- Institut für Physik, Technische Universität Ilmenau, 98693, Ilmenau, Germany
| | - Yuriy Dedkov
- Physics Department, Shanghai University, Shanghai, 200444, China
| | - Mikhail Fonin
- Department of Physics, University of Konstanz, 78457, Konstanz, Germany
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Tian YH, Huang J, Sheng X, Sumpter BG, Yoon M, Kertesz M. Nitrogen Doping Enables Covalent-Like π-π Bonding between Graphenes. NANO LETTERS 2015; 15:5482-91. [PMID: 26151153 DOI: 10.1021/acs.nanolett.5b01940] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The neighboring layers in bilayer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) π-π bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the π-π overlap across the vdW gap while the individual layers maintain their in-plane π-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.
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Affiliation(s)
- Yong-Hui Tian
- †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China
| | - Jingsong Huang
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Xiaolan Sheng
- †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China
| | - Bobby G Sumpter
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Mina Yoon
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Miklos Kertesz
- §Department of Chemistry, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057, United States
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Donati F, Dubout Q, Autès G, Patthey F, Calleja F, Gambardella P, Yazyev OV, Brune H. Magnetic moment and anisotropy of individual Co atoms on graphene. PHYSICAL REVIEW LETTERS 2013; 111:236801. [PMID: 24476294 DOI: 10.1103/physrevlett.111.236801] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Indexed: 06/03/2023]
Abstract
We report on the magnetic properties of single Co atoms on graphene on Pt(111). By means of scanning tunneling microscopy spin-excitation spectroscopy, we infer a magnetic anisotropy of K=-8.1 meV with out-of-plane hard axis and a magnetic moment of 2.2μ(B). Co adsorbs on the sixfold graphene hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their magnetic properties are very different from those of clean Co. Ab initio calculations support our results and reveal that the large magnetic anisotropy stems from strong ligand field effects due to the interaction between Co and graphene orbitals.
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Affiliation(s)
- F Donati
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland
| | - Q Dubout
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland
| | - G Autès
- Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - F Patthey
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland
| | - F Calleja
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland and Madrid Institute for Advanced Studies, IMDEA Nanoscience, Calle Faraday 9, Campus Cantoblanco, E-28049 Madrid, Spain
| | - P Gambardella
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland and Catalan Institute of Nanoscience and Nanotechnology (ICN2), UAB Campus, E-08193 Barcelona, Spain and Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| | - O V Yazyev
- Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - H Brune
- Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Switzerland
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Feng X, Kwon S, Park JY, Salmeron M. Superlubric sliding of graphene nanoflakes on graphene. ACS NANO 2013; 7:1718-1724. [PMID: 23327483 DOI: 10.1021/nn305722d] [Citation(s) in RCA: 146] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The lubricating properties of graphite and graphene have been intensely studied by sliding a frictional force microscope tip against them to understand the origin of the observed low friction. In contrast, the relative motion of free graphene layers remains poorly understood. Here we report a study of the sliding behavior of graphene nanoflakes (GNFs) on a graphene surface. Using scanning tunneling microscopy, we found that the GNFs show facile translational and rotational motions between commensurate initial and final states at temperatures as low as 5 K. The motion is initiated by a tip-induced transition of the flakes from a commensurate to an incommensurate registry with the underlying graphene layer (the superlubric state), followed by rapid sliding until another commensurate position is reached. Counterintuitively, the average sliding distance of the flakes is larger at 5 K than at 77 K, indicating that thermal fluctuations are likely to trigger their transitions from superlubric back to commensurate ground states.
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Affiliation(s)
- Xiaofeng Feng
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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