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Dedkov Y.,SPECS Surface Nano Analysis GmbH | Voloshina E.,Humboldt University of Berlin
Physical Chemistry Chemical Physics | Year: 2014

The graphene moiré structures on 4d and 5d metals, as they demonstrate both long (moiré) and short (atomic) scale ordered structures, are the ideal systems for the application of scanning probe methods. Taking graphene-Ir(111) as an example, we present the complex studies of this graphene-metal moiré-structure system by means of 3D scanning tunnelling and atomic force microscopy/spectroscopy as well as Kelvin-probe force microscopy. The results clearly demonstrate variation of the moiré and atomic scale contrast as a function of the bias voltage as well as the distance between the scanning probe and the sample, allowing one to discriminate between topographic and electronic contributions in the imaging of a graphene layer on metals. The presented results are compared with the state-of-the-art density functional theory calculations demonstrating excellent agreement between theoretical and experimental data. This journal is © 2014 the Owner Societies. Source

Graphene is an intriguing object of condensed mater physics. Discovery of its fascinating transport properties renewed the interest to the studies of graphene on metallic surfaces. That leads to the technological breakthrough showing that graphene on metals can be used as a protective layer and that its synthesis on metals is the most promising way to prepare huge graphene layers. However, all technology-related and fundamental studies of the graphene-metal interfaces require the understanding of the bonding mechanism at the interface and the consequent modifications of the electronic structure of graphene compared to the free-standing case. Here we consider two representative examples of the strongly and weakly bonded graphene on metals demonstrating how surface science methods help to understand the origin of the bonding at the graphene-metal interface. These methods help to trace all modifications in the electronic structure of graphene on the microscopic and macroscopic levels. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Dedkov Y.,SPECS Surface Nano Analysis GmbH | Voloshina E.,Humboldt University of Berlin | Fonin M.,University of Konstanz
Physica Status Solidi (B) Basic Research | Year: 2015

Graphene, a two-dimensional (2D) material with unique electronic properties, appears to be an ideal object for the application of surface-science methods. Among them, a family of scanning probe microscopy methods (STM, AFM, KPFM) and the corresponding spectroscopy add-ons provide information about the structure and electronic properties of graphene on the local scale (from μm to atoms). This review focuses on the recent applications of these microscopic/spectroscopic methods for the investigation of graphene on metals (interfaces, intercalation-like systems, graphene nanoribbons, and quantum dots, etc.). It is shown that very important information about interaction strength at the graphene/metal interfaces as well as about modification of the electronic spectrum of graphene at the Fermi level can be obtained on the local scale. The combination of these results with those obtained by other methods and comparison with recent theoretical data demonstrate the power of this approach for the investigation of the graphene-based systems. STM image of a graphene island (quantum dot) on Ir(111). Scanning probe microscopy and spectroscopy provide a unique opportunity to obtain information about the structure and electronic properties of graphene at the nanoscale. This Feature Article presents the recent most important findings on the electronic properties of graphene nanostructures on metals obtained by scanning tunnelling and atomic force microscopies and spectroscopies. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Sicot M.,University of Konstanz | Leicht P.,University of Konstanz | Zusan A.,University of Konstanz | Bouvron S.,University of Konstanz | And 6 more authors.
ACS Nano | Year: 2012

We use in situ scanning tunneling microscopy (STM) to investigate intercalation of the ferromagnetic 3d metals Ni and Fe underneath a graphene monolayer on Rh(111). Upon thermal annealing of graphene/Rh(111) with the deposited metal on top, we observe the formation of epitaxial monatomic nanoislands grown pseudomorphically on Rh(111) and covered by graphene. The size and shape of intercalated nanoislands is strongly influenced by the local spatial variation of the graphene-Rh bonding strength. In particular, the side length of the intercalated nanoislands shows maxima around discrete values imposed by the periodicity of the graphene moiré. Intercalation can be performed efficiently and without any visible damage of the graphene overlayer in the studied temperature range between 670 and 870 K. We identify the main intercalation path to be via diffusion through pre-existing lattice defects in graphene, accompanied by the second mechanism which is based on the material diffusion via metal-generated defects followed by the defect healing of the graphene lattice. We deem these graphene-capped and sharply confined ferromagnetic nanoislands interesting in the fields of spintronics and nanomagnetism. © 2012 American Chemical Society. Source

Leicht P.,University of Konstanz | Zielke L.,University of Konstanz | Bouvron S.,University of Konstanz | Moroni R.,University of Konstanz | And 5 more authors.
ACS Nano | Year: 2014

Addressing the multitude of electronic phenomena theoretically predicted for confined graphene structures requires appropriate in situ fabrication procedures yielding graphene nanoflakes (GNFs) with well-defined geometries and accessible electronic properties. Here, we present a simple strategy to fabricate quasi-free-standing GNFs of variable sizes, performing temperature programmed growth of graphene flakes on the Ir(111) surface and subsequent intercalation of gold. Using scanning tunneling microscopy (STM), we show that epitaxial GNFs on a perfectly ordered Au(111) surface are formed while maintaining an unreconstructed, singly hydrogen-terminated edge structure, as confirmed by the accompanying density functional theory (DFT) calculations. Using tip-induced lateral displacement of GNFs, we demonstrate that GNFs on Au(111) are to a large extent decoupled from the Au(111) substrate. The direct accessibility of the electronic states of a single GNF is demonstrated upon analysis of the quasiparticle interference patterns obtained by low-temperature STM. These findings open up an interesting playground for diverse investigations of graphene nanostructures with possible implications for device fabrication. © 2014 American Chemical Society. Source

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