Abstract
Si dangling bonds at the interface of quasi-free-standing monolayer graphene (QFMLG) are known to act as scattering centers that can severely affect carrier mobility. Herein, we investigate 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 graphene terrace by STM and AFM; in particular, their STM contrast varied with the bias voltage. Moreover, these defects showed characteristic STS peaks at different energies, 1.1 and 1.4 eV. The comparison of the experimental data with the DFT calculations indicates that the defects with STS peak energies of 1.1 and 1.4 eV consist of clusters of three and four Si dangling bonds, respectively. The relevance of the present results for the optimization of graphene synthesis is discussed.
Highlights
Graphene, a two-dimensional sheet of carbon atoms, is attracting considerable interest for applications in high-speed electronics, owing to its high carrier mobility [1]
The present atomic force microscopy (AFM) and scanning tunneling microscopy (STM) measurements support the assignment of the A and B features to smaller and larger vacancies, respectively
This study demonstrates that a combination of STM/AFM and density functional theory (DFT) is an ideal tool to evaluate the distribution, size, and electronic structure of atomic-size defects
Summary
A two-dimensional sheet of carbon atoms, is attracting considerable interest for applications in high-speed electronics, owing to its high carrier mobility [1]. The latter, can be severely reduced by scattering centers introduced by its supporting substrate. The buffer layer can be detached from the substrate and transformed to sp2-hybridized carbon (graphene), either by further thermal decomposition of the SiC substrate underneath the buffer layer, or by intercalation of H atoms at the interface between buffer layer and substrate [3, 4] The former approach results in the formation of epitaxial monolayer graphene (EMLG), whereas the latter produces quasifree-standing monolayer graphene (QFMLG). The carrier mobility in QFMLG (~ 6,600 cm2·V–1·s–1) [6] is lower than that in free-standing graphene, indicating the presence of residual carrier-scattering centers
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