Giant Surface Charge Density of Graphene Resolved From Scanning Tunneling Microscopy and First-Principles Theory

TL;DR

This study combines STM experiments and first-principles simulations to reveal that graphene has a surface charge density three times higher than graphite and that high-current STM enhances visualization of its honeycomb structure.

Contribution

It provides a detailed analysis of graphene's surface charge density and bonding structure using combined experimental and theoretical approaches.

Findings

Graphene's surface charge density is 300% that of graphite.

High-current STM better resolves graphene's honeycomb bonding structure.

Simulations align with experimental STM images to elucidate electron distribution.

Abstract

In this work, systematic constant-bias, variable-current scanning tunneling microscopy (STM) measurements and STM simulations from density-functional theory are made, yielding critical insights into the spatial structure of electrons in graphene. A foundational comparison is drawn between graphene and graphite, showing the surface charge density of graphene to be 300 percent that of graphite. Furthermore, simulated STM images reveal that high-current STM better resolves graphenes honeycomb bonding structure because of a retraction which occurs in the topmost dangling bond orbitals.