Quantum Interference Channeling at Graphene Edges

Yang, Heejun; Mayne, Andrew J.; Boucherit, Mohamed Seghir; Comtet, G.; Dujardin, Gérald; Kuk, Young

doi:10.1021/nl9038778

Cited by 104 publications

(148 citation statements)

References 35 publications

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“…superstructure has been reported in other experiments and always is related to armchair edges [23][24][25]. The (√3×√3)R30° periodicity of the interference pattern in the STM image can also be observed in the Fast Fourrier transform of the STM image ( Fig.…”

Section: Cnrs-laboratoire De Photonique Et De Nanostructures (Lpn)supporting

confidence: 78%

“…3(b)): we identify a first group of spots corresponding to graphene reciprocal 4 lattice (RL) (the corresponding lattice parameter is about 0.23 nm) and a second set of spots reflecting the (√3×√3)R30° superstructure. Similar interference patterns are a strong indication of a structural discontinuity of the graphene lattice at the step since it is not observed when the graphene film grows continuously across the substrate step [22][23][24]26]. …”

Section: Cnrs-laboratoire De Photonique Et De Nanostructures (Lpn)mentioning

confidence: 79%

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Epitaxial graphene on step bunching of a 6H-SiC(0001) substrate: Aromatic ring pattern and Van Hove singularities

Ridene

Wassmann

Pallecchi

et al. 2013

Applied Physics Letters

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We report scanning tunneling microscopy and spectroscopy investigation of graphene nanoribbons grown on an array of bunched steps of a 6H-SiC(0001) substrate. Our STM images of a GNR on a step terrace feature a (√3x√3)R30° pattern of aromatic rings which define our armchair nanoribbons. This is in agreement to a simulation based on density functional theory. As another signature of the one-dimensional electronic structure, in the corresponding STS spectra we find well developed, sharp Van Hove singularities.In the ongoing efforts to investigate the properties of graphene and related structures, graphene nanoribbons (GNRs) have attracted considerable attention. To a big part, this is due to the opening of an electronic band gap caused by the confinement of the electronic states in one dimension. The boundary conditions imposed by the edges, however, give rise to more phenomena than that. In this article, we address two of them, the formation of aromatic rings of delocalized π-electrons in the real space electron distribution and the appearance of Van Hove singularities (VHSs) in the local density of states (LDOS).Composed of a network of sp 2 hybridized carbon atoms, graphene can be thought of as a prototypic aromatic crystal. While three of the four valence electrons of each carbon atom are engaged in localized σ-bonds, the remaining one can form a π-bond with any of the three neighboring atoms. As long as nothing breaks the symmetry of the graphene crystal, all three options for the π-bond co-exist at the same time. When confined in narrow ribbons, however, considerations based on Clar's theory of the aromatic sextet have shown that certain π-bond configurations are preferred over others [1,2]. Depending on the edge configuration and the width of the ribbon, a distinct (√3x√3)R30° pattern of aromatic rings can form. As the states of the π-electrons lie close to the Fermi energy, this superstructure is detectable in STM measurements and has been observed near graphene edges [3]. Another effect of the one dimensional confinement of the electrons in GNRs is the appearance of divergences in the density of states (DOS) as a function of the energy, the so-called VHSs. They appear when a new sub-band in the electronic structure enters the bias window. Even though predicted theoretically, VHSs remain difficult to measure and when they are observed they are often suppressed by edge disorder [4,5].Contrary to other graphene growth methods, graphitization of SiC does not require a graphene transfer since SiC represents itself a suitable substrate for high power, high frequency, and opto-electronic devices [6]. The structure and electronic properties of graphene grown on SiC, however, strongly depend on the presence of steps on the substrate [6]. These steps, concentrated or bunched in narrow regions separated by larger atomically flat (0001) terraces, are known to be detrimental for the mobility of graphene. On the other hand, since the widths of the terraces are homogeneous to a high degree [7], they have proven to be us...

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Section: Cnrs-laboratoire De Photonique Et De Nanostructures (Lpn)supporting

confidence: 78%

Section: Cnrs-laboratoire De Photonique Et De Nanostructures (Lpn)mentioning

confidence: 79%

Epitaxial graphene on step bunching of a 6H-SiC(0001) substrate: Aromatic ring pattern and Van Hove singularities

Ridene

Wassmann

Pallecchi

et al. 2013

Applied Physics Letters

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show abstract

“…We emphasize that a few publications have tried so far to give a description of the different features in the experimental FT-LDOS images of epitaxial graphene. 27,28,30,31 However, a poor resolution in k space was partly limiting such analysis. In a report published in 2008, some of us have shown that it was possible to evidence fine structures in FT-LDOS data with improved quality.…”

Section: High-resolution Stm Results On Monolayer Graphene On Sicmentioning

confidence: 99%

“…[27][28][29][30][31][32][34][35][36][37][38][39][40][41][42] Because of the topology of the FS pockets, coupling between states with opposite q F in each pocket [ Fig. 1(d)] is highly favored.…”

Section: Quasiparticle Scattering In Graphene: Intravalley and Imentioning

confidence: 99%

Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy

et al. 2012

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Pseudospin, an additional degree of freedom emerging in graphene as a direct consequence of its honeycomb atomic structure, is responsible for many of the exceptional electronic properties found in this material. This paper is devoted to providing a clear understanding of how graphene's pseudospin impacts the quasiparticle interferences of monolayer (ML) and bilayer (BL) graphene measured by low-temperature scanning tunneling microscopy and spectroscopy. We have used this technique to map, with very high energy and space resolution, the spatial modulations of the local density of states of ML and BL graphene epitaxially grown on SiC(0001), in presence of native disorder. We perform a Fourier transform analysis of such modulations including wave vectors up to unit vectors of the reciprocal lattice. Our data demonstrate that the quasiparticle interferences associated to some particular scattering processes are suppressed in ML graphene, but not in BL graphene. Most importantly, interferences with 2q F wave vector associated to intravalley backscattering are not measured in ML graphene, even on the images with highest resolution where the graphene honeycomb pattern is clearly resolved. In order to clarify the role of the pseudospin on the quasiparticle interferences, we use a simple model which nicely captures the main features observed in our data. The model unambiguously shows that graphene's pseudospin is responsible for such suppression of quasiparticle interference features in ML graphene, in particular for those with 2q F wave vector. It also confirms scanning tunneling microscopy as a unique technique to probe the pseudospin in graphene samples in real space with nanometer precision. Finally, we show that such observations are robust with energy and obtain with great accuracy the dispersion of the π bands for both ML and BL graphene in the vicinity of the Fermi level, extracting their main tight-binding parameters.

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“…Nanometer-scale STM measurements, yielding both local density of states (LDOS) and topographic details, are extensively used both theoretically [9][10][11][12][13][14][15][16] and experimentally [17][18][19][20][21][22] in the study of graphene. However, the STM measures only local properties, whereas we often want to obtain information about the transport properties for electrons traversing the sample.…”

Section: Introductionmentioning

confidence: 99%

Dual-probe spectroscopic fingerprints of defects in graphene

et al. 2014

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Recent advances in experimental techniques emphasize the usefulness of multiple scanning probe techniques when analyzing nanoscale samples. Here, we analyze theoretically dual-probe setups with probe separations in the nanometer range, i.e., in a regime where quantum coherence effects can be observed at low temperatures. In a dual-probe setup the electrons are injected at one probe and collected at the other. The measured conductance reflects the local transport properties on the nanoscale, thereby yielding information complementary to that obtained with a standard one-probe setup (the local density of states). In this work we develop a real-space Green's function method to compute the conductance. This requires an extension of the standard calculation schemes, which typically address a finite sample between the probes. In contrast, the developed method makes no assumption of the sample size (e.g., an extended graphene sheet). Applying this method, we study the transport anisotropies in pristine graphene sheets, and analyze the spectroscopic fingerprints arising from quantum interference around single-site defects, such as vacancies and adatoms. Furthermore, we demonstrate that the dual-probe setup is a useful tool for characterizing the electronic transport properties of extended defects or designed nanostructures. In particular, we show that nanoscale perforations, or antidots, in a graphene sheet display Fano-type resonances with a strong dependence on the edge geometry of the perforation.

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Quantum Interference Channeling at Graphene Edges

Cited by 104 publications

References 35 publications

Epitaxial graphene on step bunching of a 6H-SiC(0001) substrate: Aromatic ring pattern and Van Hove singularities

Epitaxial graphene on step bunching of a 6H-SiC(0001) substrate: Aromatic ring pattern and Van Hove singularities

Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy

Dual-probe spectroscopic fingerprints of defects in graphene

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