Electronic decoupling of an epitaxial graphene monolayer by gold intercalation

Gierz, Isabella; Suzuki, Takayuki; Weitz, R. Thomas; Lee, Dong Su; Krauß, Benjamin; Riedl, Christian; Starke, Ulrich; Höchst, H.; Smet, J. H.; Ast, Christian R.; Kern, Klaus

doi:10.1103/physrevb.81.235408

Cited by 227 publications

(234 citation statements)

References 37 publications

(28 reference statements)

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“…It was speculated whether the latter phase shows p-doping [19]. The existence of an n-doped phase shifted by ∼ −0.85 eV and a slightly p-doped phase has been confirmed subsequently by ARPES performed in the near-Fermi-energy region [20].In the present work, we study Au intercalation by spin-ARPES and core-level photoemission. We confirm the n-and p-doped phases and study how the hybridization between the Dirac cone and Au states changes between the two phases.…”

mentioning

confidence: 98%

“…In the context of a possible p-doping of graphene by metals, the intercalation of Au under graphene on SiC has already been studied [19,20], which serves as starting point for our search for enhanced spin-orbit splittings in this system. Scanning tunneling microscopy (STM) and spectroscopy (STS) [19] reveal two stages of Au intercalation: intercalation of Au clusters without change of the n-type doping of graphene on SiC and intercalation of 1 2 monolayer (ML) of Au with a 2 √ 3×2 √ 3R30…”

Section: Introductionmentioning

confidence: 99%

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Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Marchenko

Varykhalov

Sánchez-Barriga

et al. 2016

Applied Physics Letters

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Intercalation of Au can produce giant Rashba-type spin-orbit splittings in graphene but this has not yet been achieved on a semiconductor substrate. For graphene/SiC(0001), Au intercalation yields two phases with different doping. Here, we report the preparation of an almost pure p-type graphene phase after Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9 eV binding energy. We show that this giant splitting is due to hybridization and much more limited in energy and momentum space than for Au-intercalated graphene on Ni. In a future spintronics, graphene could be used in various ways: as efficient leads for spin currents due to low spin-orbit interaction and large spin relaxation lengths [1], as ferromagnetic graphene due to a proximity magnetization [2], as spin filter when a large Rashba type spin-orbit interaction and a band gap at the Dirac point are imposed by a substrate [3], or when the spin-orbit interaction is strongly enhanced by covalently bonded adatoms [4]. The Rashba effect on a graphene Dirac cone leads to a complex band topology with a gapped and an ungapped cone similar to spinless bilayer graphene [5,6]. It has been shown by ARPES that for Au-intercalated graphene/Ni(111) the Dirac cone is intact [7] and gapless [8]. A giant Rashba splitting of ∼ 100 meV was found for graphene/Au/Ni(111) [9].On light elements, the spin-orbit splitting of graphene cannot be resolved in experiment, this is the case with Ni(111) and Co(0001) [10,11]. Where, instead, an unexpected Dirac point forms at higher binding energy as part of a pair of bonding and antibonding Dirac cones [12]. These cones have been found to be highly spin polarized by the exchange interaction from the substrate [13,14].The interfaces of graphene with metals are structurally rather well defined, and the intercalation of Au is driven by the transition metal substrate. The creation of the spinorbit interaction in the graphene is well understood based on spin-dependent hybridization with d-states of the substrate. This is the case for graphene/Au/Ni(111) [9] and is confirmed indirectly by the vanishing spin-orbit splitting of the graphene-Bi interface because atomic numbers of Bi and Au are similar but hybridization with d-states is possible only for Au [15]. A similar hybridization causes the ∼ 50 meV spin-orbit splitting for graphene/Ir (111) [16].To make the aforementioned effects useful for spintronics, they have to be confirmed on an insulating substrate such as SiC because otherwise the metallic substrate will dominate charge and spin transport. On bare SiC, graphene does not show an enhanced spin-orbit splitting as has been clarified by spin-resolved photoemission [17]. Recently, a spin-orbit splitting of 17 meV has been measured for graphene on the semiconductor WS 2 [18].In the context of a possible p-doping of graphene by metals, the intercalation of Au under graphene on SiC has already been studied [19,20], which serves as starting point for our search for enhanced spin-orbit splittings in this s...

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mentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Marchenko

Varykhalov

Sánchez-Barriga

et al. 2016

Applied Physics Letters

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“…Therefore this buffer layer is considered to be a main obstacle to the development of future electronic devices based on graphene grown on SiC(0001). Nonetheless, earlier studies have demonstrated that this buffer layer can be decoupled from the substrate and transformed into a graphene layer by hydrogen (H) [6,[10][11][12], gold (Au) [13], oxygen (O 2 ) [14] and lithium (Li) [15][16] intercalation.…”

Section: Introductionmentioning

confidence: 99%

Studies of Li intercalation of hydrogenated graphene on SiC(0001)

et al. 2012

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The effects of Li deposition on hydrogenated bilayer graphene on SiC(0001) samples, i.e. on quasi-freestanding bilayer graphene samples is studied using low energy electron microscopy, micro-low-energy electron diffraction and photoelectron spectroscopy. After deposition, some Li atoms form islands on the surface creating defects that are observed to disappear after annealing. Some other Li atoms are found to penetrate through the bilayer graphene sample and into the interface where H already resides. This is revealed by the existence of shifted components, related to H-SiC and Li-SiC bonding, in recorded core level spectra. The Dirac point is found to exhibit a rigid shift to about 1.25 eV below the Fermi level, indicating strong electron doping of the graphene by the deposited Li.

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Section: Introductionmentioning

confidence: 99%

“…Another option is to intercalate metal under graphene; this approach is typically used to decouple the graphene and the substrate. [9][10][11] However, a uniform intercalation on a large scale is difficult to achieve.We also note that in case of the Si/SiO 2 substrate, the Raman signal can be also enhanced by interference effects. [12] Nevertheless, the enhancement is not sufficient to observe features of functional groups.…”

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confidence: 99%

Surface‐enhanced Raman spectra on graphene

Weis

Vejpravová

Verhagen

et al. 2017

J Raman Spectroscopy

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Surface-enhanced Raman spectroscopy is a valuable tool for inspection of trace concentrations of various molecules; hence, this method has a great potential for characterization of functionalised graphene. However, to make this method a reliable analytical tool, the influence of the metal-graphene interactions on Raman spectra of the graphene must be understood. Here, the surface-enhanced Raman spectra of exfoliated single-layer graphene covered with gold or silver thin layers were studied. The metal-graphene interactions resulted in the broadening of the G mode and the 2D mode of graphene. A change of the 2D mode dispersion was also observed. The effects were found to be weaker for the silver layer; however, the Raman signal enhancement of the graphene features was found to be significantly stronger in case of the silver layer. Various scenarios of the observed effects are discussed: graphene-plasmon interaction, charge transfer between the metal and graphene, and selective enhancement at the lattice and topographic defects. Copyright © 2017 John Wiley & Sons, Ltd.Keywords: charge transfer; graphene; graphene-plasmon interaction; metal-graphene interaction; SERS IntroductionMetals such as gold and silver are known to strongly enhance the Raman signal of pristine graphene. [1,2] In particular, the approach is extremely important for the chemically functionalized graphene samples because it allows to identify the functional groups on the graphene surface. [3] However, it is also known that graphene may strongly interact with the metals, and this interaction is also mirrored in the Raman spectra. [4] Consequently, it is important to follow these effects.Raman spectra of a pristine graphene typically consist of the G mode, which appears at about 1,580 cm −1 , and the 2D mode, which is significantly dispersive and its wavenumber increases with the laser excitation energy. The dispersion comes from the slope of the Dirac cone; therefore, changes in the dispersion reflect changes in the electronic structure of the graphene. [5,6] In case that structural imperfections are present in a graphene sample, one can also observe the defect scattering related D and D' modes at around 1,350 and 1,620 cm −1 , respectively. As reported by several authors previously, the enhancement of a particular Raman mode of graphene depends on the excitation energy of the laser and plasmonic characteristics of the metallic structure in contact with the graphene, and consequently, the enhancement factors for the D, D', G, and 2D modes can be very different. [7,8] Moreover, not only the kind of metal but also the shape, dimensions, and mutual geometry of the metallic structure and graphene are of utmost importance.In a typical experiment, the enhancement of the Raman signal can be achieved by deposition of a thin layer of silver or gold or their nanoparticles over the graphene. This geometry, however, reduces intensity of the incoming light, and also, the scattered light is partly absorbed by the metal. Another option is to intercalate metal un...

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Electronic decoupling of an epitaxial graphene monolayer by gold intercalation

Cited by 227 publications

References 37 publications

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Rashba splitting of 100 meV in Au-intercalated graphene on SiC

Studies of Li intercalation of hydrogenated graphene on SiC(0001)

Surface‐enhanced Raman spectra on graphene

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