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Sforzini, Jessica; Nemec, Lydia; Denig, Tobias; Stadtmüller, Benjamin; Lee, T.-L.; Kumpf, Christian; Soubatch, Serguei; Starke, Ulrich; Rinke, Patrick; Blüm, Volker; Bocquet, François C.; Tautz, F. Stefan

doi:10.1103/physrevlett.114.106804

Cited by 81 publications

(63 citation statements)

References 47 publications

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“…As the lattice parameter of the latter, one usually considers the ideal graphene value 2.46 Å, leading to a consensus supercell of ∼3.2 nm side, corresponding to 6 √ 3 × 6 √ 3 R30 of SiC and 13 × 13 of graphene (see Figure 2A). This symmetry and the corresponding supercell are considered the standard model system (Mallet et al, 2007;Kim et al, 2008;Sforzini et al, 2015) for calculations, and are compatible with the experimental observations of MLG 1 (Varchon et al, 2008). The picture is consistent, considering that the level of residual mismatch of graphene in this supercell is very small, compatible with the soft corrugation observed in MLG.…”

Section: The Moiré Pattern: Unique or Not Unique?supporting

confidence: 82%

From the Buffer Layer to Graphene on Silicon Carbide: Exploring Morphologies by Computer Modeling

2019

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Epitaxial graphene grown by thermal Si decomposition of Silicon Carbide appears in different morphological variants, depending on the production conditions: the strongly rugged buffer layer, retaining a considerable amount of sp 3 hybridized buffer layer, the softly corrugated graphene monolayer and the rather flat quasi free standing monolayer with sparse small pits pinned to localized electronic states. Therefore, graphene on SiC is not a single material, but a set of materials with different morphologies depending on the environmental conditions during the synthesis. In all cases the distortion from the ideal flat structure seem to follow to some extent specific symmetries, which appear to preserve some memory of the interaction with the SiC bulk, even in the cases in which the sheet is substantially decoupled from it. Defects bear interesting properties, e.g., localized hot spots of reactivity and localized electronic states with specific energy depending on their nature and morphology, while their possible symmetric location is an added value for applications. Therefore, being capable of controlling the morphology, concentration, symmetry and location of the defects would allow tailoring this material for specific applications. Based on ab initio calculations and simulations, we first describe in detail the morphology of the different systems, and subsequently, we formulate hypotheses on the relationship between morphology and the formation process. We finally suggest future simulation studies capable of revealing the still unclear steps. These should give indication on how to tune the environmental conditions to control the final morphology of the sample and specifically design this material.

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Section: The Moiré Pattern: Unique or Not Unique?supporting

confidence: 82%

From the Buffer Layer to Graphene on Silicon Carbide: Exploring Morphologies by Computer Modeling

2019

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“…21 It also exhibits very low buckling and homogeneous electron density at the interface. 21 Beside hydrogen, also annealing in oxygen, 22 rapid cooling 23 or ion implantation 24 have been shown to turn buffer layer into QFSMLG. However, oxygen annealing and ion implantation can lead to defect formation in graphene and rapid cooling is not suitable for fabrication of electronic devices on large scales.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen intercalation of epitaxial graphene and buffer layer probed by mid-infrared absorption and Raman spectroscopy

2018

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We have measured optical absorption in mid-infrared spectral range on hydrogen intercalated single layer epitaxial graphene and buffer layer grown on silicon face of SiC. We have used attenuated total reflection geometry to enhance absorption related to the surface and SiC/graphene interface. The Raman spectroscopy is used to show presence of buffer layer and single layer graphene prior to intercalation. We also present Raman spectra of quasi free standing monolayer and bilayer graphene after hydrogen intercalation at temperatures between 790 and 1510°C. We have found that although the Si-H bonds form at as low temperatures as 790°C, the well developed bond order has been reached only for samples intercalated at temperatures exceeding 1000°C. We also study temporal stability of hydrogen intercalated samples stored in ambient air. The optical spectroscopy shows on a formation of silyl and silylene groups on the SiC/graphene interface due to the residual atomic hydrogen left from the intercalation process.

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“…The C-Si z-spacing, ∆ Si-C , in the SiC bilayer below BG o is 30% shorter compared to a bulk SiC bilayer and half the distance predicted by ab initio calculations in a bulk terminated surface with a BG ML +ML film. 12 It is likely that the vacancies in the top SiC bilayer lead to the additional bulk peak C B in the 5-component C1s spectra in Figs. 5(b) and (d).…”

Section: Z-zs1(å) σ(å) θ(Mlg)mentioning

confidence: 99%

“…Ab initio calculations using a ( √ 3× √ 3) SiC R30 cell find a wide bandgap buffer while calculations on larger, experimentally observed (6 √ 3 × 6 √ 3) SiC R30 • cells 10,11 find metallic states running through the Fermi Energy (E F ). [5][6][7] The applicability of these early calculations is problematic because they all assumed that the SiC surface is bulk terminated, 7,8,12 an assumption that we now know is incorrect. Recent x-ray diffraction studies have demonstrated that the buffer-SiC interface is not commensurate with SiC.…”

Section: Introductionmentioning

confidence: 99%

Structure and evolution of semiconducting buffer graphene grown on SiC(0001)

et al. 2017

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Using highly controlled coverages of graphene on SiC(0001), we have studied the structure of the first graphene layer that grows on the SiC interface. This layer, known as the buffer layer, is semiconducting. Using x-ray reflectivity and x-ray standing waves analysis we have performed a comparative study of the buffer layer structure with and without an additional monolayer graphene layer above it. We show that no more than 26% of the buffer carbon is covalently bonded to Si in the SiC interface. We also show that the top SiC bilayer is Si depleted and is the likely the cause of the incommensuration previously observed in this system. When a monolayer graphene layer forms above the buffer, the buffer layer becomes less corrugated with signs of a change in the bonding geometry with the SiC interface. At the same time, the entire SiC interface becomes more disordered, presumably due to entropy associated with the higher growth temperature.

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Approaching Truly Freestanding Graphene: The Structure of Hydrogen-Intercalated Graphene on6H−SiC(0001)

Cited by 81 publications

References 47 publications

From the Buffer Layer to Graphene on Silicon Carbide: Exploring Morphologies by Computer Modeling

From the Buffer Layer to Graphene on Silicon Carbide: Exploring Morphologies by Computer Modeling

Hydrogen intercalation of epitaxial graphene and buffer layer probed by mid-infrared absorption and Raman spectroscopy

Structure and evolution of semiconducting buffer graphene grown on SiC(0001)

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