Correlation between morphology and transport properties of quasi-free-standing monolayer graphene

Murata, Yuya; Mashoff, T.; Takamura, Makoto; Tanabe, Setsuhisa; Hibino, Hiroki; Beltram, Fabio; Heun, S.

doi:10.1063/1.4902988

Cited by 22 publications

(41 citation statements)

References 15 publications

(21 reference statements)

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“…This is more evident in the BL and MLG, where the moiré pattern reflects a super periodicity, which was initially recognized as "quasi" 6 × 6 of SiC, and attributed to the mismatch between the SiC and graphene lattice parameters. Interestingly, a similar symmetry can be observed also in QFMLG, especially if obtained under slow hydrogenation conditions: vacancies seems to prefer locating on an hexagonal super-lattice of size ∼1.8 nm (still corresponding to 6 × 6), although not all the sites are occupied (the concentration and shape of vacancies is very variable, depending on the temperature and pressure of hydrogen during the process) (Murata et al, 2014;Cavallucci and Tozzini, 2016). This indicates that, in spite of the decoupling operated by the intercalating layer, the QFMLG preserves some memory of the interaction with the substrate.…”

supporting

confidence: 60%

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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confidence: 60%

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

2019

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“…The observed surface structure is not new in literature for intercalated samples. Also for H-, 43 Na-, 44 and F-intercalated epitaxial graphene on SiC 45 these surface features have been observed. From literature it is well known that about 30% of the C-atoms of the buffer layer form covalent bonds to Si atoms of the SiC substrate, which corresponds to 0.3 ML.…”

Section: Resultsmentioning

confidence: 75%

“…If we compare these results to the well-studied case of H-intercalation of G/SiC, we note some differences. Hydrogen intercalation performed under typical process conditions (H-pressure 1013 mbar and temperature 600− 1200 • C) 43 occurs almost instantaneous and complete. 58 This means that once a path is created (either at the step edge or at a defect site), the entire terrace intercalates at once.…”

Section: Discussionmentioning

confidence: 99%

Li-intercalated graphene on SiC(0001): An STM study

et al. 2017

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We present a systematical study via scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) on the effect of the exposure of Lithium (Li) on graphene on silicon carbide (SiC). We have investigated Li deposition both on epitaxial monolayer graphene and on buffer layer surfaces on the Si-face of SiC. At room temperature, Li immediately intercalates at the interface between the SiC substrate and the buffer layer and transforms the buffer layer into a quasi-free-standing graphene. This conclusion is substantiated by LEED and STM evidence. We show that intercalation occurs through the SiC step sites or graphene defects. We obtain a good quantitative agreement between the number of Li atoms deposited and the number of available Si bonds at the surface of the SiC crystal. Through STM analysis, we are able to determine the interlayer distance induced by Li-intercalation at the interface between the SiC substrate and the buffer layer.

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“…[7] In a previous report, we studied the correlation between the morphology of QFMLG and T H , the substrate temperature during H intercalation. [8] In scanning tunneling microscopy (STM) images measured at room temperature on QFMLG samples formed at T H = 600 and 800 °C, depressions with a width of 1 nm were observed on flat terraces. These depressions distribute with the periodicity of the SiC(0001) quasi-(6×6) reconstruction, i.e., with the periodicity of the buffer layer.…”

mentioning

confidence: 99%

“…It was also found that the density of these 3 depressions on a QFMLG sample formed at T H = 1000 °C is two orders of magnitude smaller than that on samples formed at T H = 600 and 800 °C. [8] As T H increases, the dissociation of H 2 molecules, the intercalation of H atoms, and their diffusion along the graphene-substrate interface are promoted, and this leads to a better H intercalation, i.e., less Si dangling-bond formation. [10] A similar distribution of Si dangling bonds at the interface of quasi-free standing bilayer graphene was reported by noncontact scanning nonlinear dielectric potentiometry.…”

mentioning

confidence: 99%

Atomic and electronic structure of Si dangling bonds in quasi-free-standing monolayer graphene

Murata¹,

Cavallucci²,

Tozzini³

et al. 2017

Nano Res.

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Si dangling bonds without H termination at the interface of quasi-free standing monolayer graphene (QFMLG) are known scattering centers that can severely affect carrier mobility. In this report, we study the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM), and density functional theory (DFT) calculations. Two types of defects with different contrast were observed on a flat terrace by STM and AFM.Their STM contrast varies with bias voltage. In STS, they showed characteristic peaks at different energies, 1.1 and 1.4 eV. Comparison with DFT calculations indicates that they correspond to clusters of 3 and 4 Si dangling bonds, respectively. The relevance of these results for the optimization of graphene synthesis is discussed.

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Correlation between morphology and transport properties of quasi-free-standing monolayer graphene

Cited by 22 publications

References 15 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

Li-intercalated graphene on SiC(0001): An STM study

Atomic and electronic structure of Si dangling bonds in quasi-free-standing monolayer graphene

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