Direct Visualization of Native Defects in Graphite and Their Effect on the Electronic Properties of Bernal-Stacked Bilayer Graphene

TL;DR

This study reveals that graphite used in graphene devices contains native defects that significantly impact electronic properties, with detailed microscopy and theoretical analysis showing their role in scattering and mobility limitations.

Contribution

It provides the first direct visualization and quantification of native defects in graphite and links these defects to electronic scattering in bilayer graphene.

Findings

Native defect concentration is 6.6×10^8 cm^-2.

Defects cause gate-dependent intravalley scattering.

Defects limit low-temperature mobility.

Abstract

Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be defect free. We report here scanning tunneling microscopy results that show graphite commonly used to prepare graphene devices can contain a significant amount of native defects. Extensive scanning of the surface allows us to determine the concentration of native defects to be 6.6$\times$10$^8$ cm$^{-2}$. We further study the effects of these native defects on the electronic properties of Bernal-stacked bilayer graphene. We observe gate-dependent intravalley scattering and successfully compare our experimental results to T-matrix-based calculations, revealing a clear carrier density dependence in the distribution of the scattering vectors. We also present a technique for evaluating the spatial distribution of short-scale scattering. A theoretical analysis based on the Boltzmann transport equation predicts that the dilute native defects identified here are an important extrinsic source of scattering, ultimately setting the mobility at low temperatures.