Local electroexfoliation of graphene with a STM tip

TL;DR

This study demonstrates a systematic method for local electroexfoliation of graphene using an STM tip, combining experiments and simulations to understand the process and enabling precise surface modifications of layered materials.

Contribution

It introduces a novel electroexfoliation technique with a detailed mechanistic understanding through experiments and simulations, advancing surface modification methods for layered materials.

Findings

Triangular graphene flakes can be created by electroexfoliation at terrace edges.

A two-step process involving voltage ramping and tip scanning is essential.

Electrostatic charges weaken interlayer interactions, facilitating exfoliation.

Abstract

Graphite surfaces can be manipulated by several methods to create graphene structures of different shapes and sizes. Scanning tunneling microscopy (STM) can be used to create these structures either through mechanical contact between the tip and the surface or through electro-exfoliation. In the latter, the mechanisms involved in the process of exfoliation with an applied voltage are not fully understood. Here we show how a graphite surface can be locally exfoliated in a systematic manner by applying an electrostatic force with a STM tip at the edge of a terrace, forming triangular flakes several nanometers in length. We demonstrate, through experiments and simulations, how these flakes are created by a two-step process: first a voltage ramp must be applied at the edge of the terrace, and then the tip must be scanned perpendicularly to the edge. Ab-initio electrostatic calculations reveal that the presence of charges on the graphite surface weakens the interaction between layers allowing for exfoliation at voltages in the same range as those used experimentally. Molecular dynamics simulations show that a force applied locally on the edge of a step produces triangular flakes such as those observed under STM. Our results provide new insights towards surface modification that can be extended to other layered materials.