Atomic and Electronic Structure of Si Dangling Bonds in Quasi-Free-Standing Monolayer Graphene

TL;DR

This study investigates the atomic and electronic structures of silicon dangling bonds in quasi-free-standing monolayer graphene, revealing their impact on electronic properties and providing insights for improved graphene synthesis.

Contribution

The paper combines experimental STM/STS and AFM with DFT calculations to identify and characterize Si dangling bond clusters in QFMLG, advancing understanding of defect-related scattering centers.

Findings

Identified two types of Si dangling bond clusters with distinct electronic signatures.

Observed bias-dependent contrast variations in STM images.

Linked defect structures to specific electronic states at 1.1 and 1.4 eV.

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.