Screening of electron-phonon coupling in graphene on Ir(111)

Endlich, M.; Molina-Sánchez, Alejandro; Wirtz, Ludger; Kröger, J.

doi:10.1103/physrevb.88.205403

Cited by 43 publications

(76 citation statements)

References 37 publications

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“…Cu) but also an intensity enhancement associated with the constructive interference between the graphene and the Si, separated by the silicon oxide 26,27 . Quenching of the Raman modes, which has been reported for graphene forming a coherent epitaxial (1×1) phase on the lattice matching Co(0001) 28 surface and ascribed to the hybridization of graphene's π orbitals with the metal d ones 29,30 , is here absent. Presumably, the interaction between graphene and cobalt is much weaker in the configurations that we have observed, which are not necessarily coherent epitaxial systems, nor do they involve the (0001) plane of cobalt (the foils are polycrystalline).…”

mentioning

confidence: 70%

“…1d, because the average slope of 2.2 is within the range expected for both uniaxial and equibiaxial cases. 30 Taking into account the small size of the analyzed monolayer areas on our predominantly multilayered samples, non-equibiaxial strain is the expected dominant strain state. We will address this in more detail below, but first we estimate the maximum strain in the sample, considering two extreme cases.…”

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confidence: 99%

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Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag

et al. 2015

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We measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by chemical vapor deposition (CVD), by combining microscopy techniques and local vibrational characterization. These strain fields have magnitudes of several tenths of a percent and extend across micrometer distances. The nonlinear shear-lag model remarkably captures these strain fields in terms of the graphene-substrate interaction and provides a complete understanding of strain-relieving wrinkles in graphene for any level of graphene-substrate coherency.

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mentioning

confidence: 70%

mentioning

confidence: 99%

Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag

et al. 2015

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“…Nevertheless, the well-known LDA overestimates the (weak) covalent part of the interlayer bonding and compensates thus the missing vdW forces yielding a bound ground state for most layered materials. This explains the success of LDA in obtaining the geometry of many layered materials such as graphite [75], boron nitride [76,77] or graphene on different substrates [78,79,80]. The good performance of LDA in layered materials (although fortuitous) has made this approximation widely used in the calculations of structural properties.…”

Section: Structural Propertiesmentioning

confidence: 99%

“…For graphene, this has been widely explored: the so-called 2D line in the spectra splits into sub-peaks when going from the single to the multi-layer case [94,95]. Last but not least, the 2D-line also changes position as a function of the underlying substrate [96,97,98,80]. All these features are related to the double-resonant nature [99] of Raman scattering in graphene and on the dependence of the highest optical mode on the screening.…”

Section: Structural Propertiesmentioning

confidence: 99%

Vibrational and optical properties of MoS2: From monolayer to bulk

Molina-Sánchez

Hummer

Wirtz

2015

Surface Science Reports

216

167

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Molybdenum disulfide, MoS 2 , has recently gained considerable attention as a layered material where neighboring layers are only weakly interacting and can easily slide against each other. Therefore, mechanical exfoliation allows the fabrication of single and multi-layers and opens the possibility to generate atomically thin crystals with outstanding properties. In contrast to graphene, it has an optical gap of 1.9 eV. This makes it a prominent candidate for transistor and opto-electronic applications. Single-layer MoS 2 exhibits remarkably different physical properties compared to bulk MoS 2 due to the absence of interlayer hybridization. For instance, while the band gap of bulk and multi-layer MoS 2 is indirect, it becomes direct with decreasing number of layers. In this review, we analyze from a theoretical point of view the electronic, optical, and vibrational properties of single-layer, few-layer and bulk MoS 2 . In particular, we focus on the effects of spinorbit interaction, number of layers, and applied tensile strain on the vibrational and optical properties. We examine the results obtained by different methodologies, mainly ab initio approaches. We also discuss which approximations are suitable for MoS 2 and layered materials. The effect of external strain on the band gap of single-layer MoS 2 and the crossover from indirect to direct band gap is investigated. We analyze the excitonic effects on the absorption spectra. The main features, such as the double peak at the absorption threshold and the high-energy exciton are presented. Furthermore, we report on the phonon dispersion relations of single-layer, few-layer and bulk MoS 2 . Based on the latter, we explain the behavior of the Raman-active A 1g and E 1 2g modes as a function of the number of layers. Finally, we compare theoretical and experimental results of Raman, photoluminescence, and optical-absorption spectroscopy.

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“…The question then arises what the origin of the strong down-shift of the 2D-line in KC 36 is. Possibly, the environment of the uncharged layers, leads to a modification in the strong Kohn anomaly of the highest optical branch at K. These effects include a possible reduction of the electron-phonon coupling due to the (residual) charging [124], or a partial suppression of the Kohn anomaly due to hybridization with the outer layers (similar to the case when graphene gets closer to a Ni (111) surface [125]), or attenuation of the Kohn-anomaly via dielectric [126] screening or metallic screening [127,128]. However, all of these mechanisms would lead rather to an upshift of the 2D-line and not a strong down-shift.…”

Section: Raman Study Of Charge Transfer and Strain In Highly Staged Gmentioning

confidence: 99%

Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers

Chacón-Torres

Wirtz

Pichler

2014

Physica Status Solidi (b)

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Graphite intercalation compounds (GICs) are an interesting and highly studied field since 1970's. It has gained renewed interest since the discovery of superconductivity at high temperature for CaC 6 and the rise of graphene. Intercalation is a technique used to introduce atoms or molecules into the structure of a host material. Intercalation of alkali metals in graphite has shown to be a controllable procedure recently used as a scalable technique for bulk production of graphene, and nano-ribbons by induced exfoliation of graphite. It also creates supra-molecular interactions between the host and the intercalant, inducing changes in the electronic, mechanical, and physical properties of the host. GICs are the mother system of intercalation also employed in fullerenes, carbon nanotubes, graphene, and carbon-composites. We will show how a combination of Raman and ab-initio calculations of the density and the electronic band structure in GICs can serve as a tool to elucidate the electronic structure, electron-phonon coupling, charge transfer, and lattice parameters of GICs and the graphene layers within. This knowledge of GICs is of high importance to understand superconductivity and to set the basis for applications with GICs, graphene and other nano-carbon based materials like nanocomposites in batteries and nanoelectronic devices.

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Screening of electron-phonon coupling in graphene on Ir(111)

Cited by 43 publications

References 37 publications

Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag

Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag

Vibrational and optical properties of MoS2: From monolayer to bulk

Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers

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