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

Abstract

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.

Combining scanning tunneling microscope (STM) imaging and local manipulation to probe the high dose oxidation structure of the Si(111)-7×7 surface

“…The STM can induce molecular manipulation via local injection of electrons directly into single atoms and molecules. This manipulation may induce weakening (diffusion, switching) or breaking (desorption, dissociation, and transformation) of bonds, probing the chemistry and energetics of the surface [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Engineering 3D Graphene-Based Materials: State of the Art and Perspectives

“…Alternatively, the BL can be detached by intercalating H [108] or metals [109], obtaining the Quasi-Free-Standing Monolayer graphene (QFMLG) [110]. This is ideally flat, but displays in reality localized concavities, occupying the sites of a lattice roughly corresponding to 6 × 6 of SiC [111] with~1.8 nm side, which were associated with vacancies of H in the intercalating layer [112]. The electronic structure is strongly affected by these defects, since Si dangling bonds produce electronic states localized near the Fermi level [113].…”

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

“…7H type vacancies are circled in white. Data are taken with permission from Cavallucci and Tozzini (2016), , Murata et al (2018) and recast in different form.…”

“…Finally, the QFMLG is very weakly interacting with the substrate and is basically flat, except in correspondence of defects (vacancies) of the H (or metal) intercalating layer, where it increasingly bends inward as the vacancy size increases (Figure 1B, bottom). Additionally, localized electronic states form in correspondence of the vacant sites, whose energy and "shape" (as observed by scanning tunneling microscopy-STMexperiments) depend on the number and relative location of the vacant sites ( Figure 1C) Murata et al, 2018). This variety of morphologies suggests a number of interesting applications: the buffer layer sharp crests are areas in which the regularity of the delocalized π system is locally destroyed or at least disturbed, and therefore likely to be highly reactive sites, prone to adhesion of atomic species [e.g., hydrogen (Goler et al, 2013b)] or other chemicals for functionalization.…”

“…The calculations of MLG (top) and the last one of the QFMLG (bottom, foreground) are obtained with the 6 √ 3 × 6 √ 3 R30 SiC /13 × 13 gr supercell, the others with the √ 31 × √ 31R8.95 SiC 7 × 7 R21.787 gr . Plots and pictures of (B,C) are reproduced with permission for adapting or using data from Tozzini (2016, 2018), , Murata et al (2018).…”