Manipulation of the graphene surface potential by ion irradiation

TL;DR

This paper demonstrates that swift heavy ion irradiation can locally modify the surface potential of graphene, effectively doping it from n-type to p-type, with persistent effects due to implanted atoms, offering a new method for charge manipulation.

Contribution

It introduces a novel ion irradiation technique to locally and permanently alter the electronic properties of graphene by doping through implanted atoms.

Findings

Ion irradiation creates localized surface tracks in graphene.

Surface potential can be shifted by approximately 400 meV.

The doping effect remains stable after heating to 500°C.

Abstract

We show that the work function of exfoliated single layer graphene can be modified by irradiation with swift (E_{kin}=92 MeV) heavy ions under glancing angles of incidence. Upon ion impact individual surface tracks are created in graphene on SiC. Due to the very localized energy deposition characteristic for ions in this energy range, the surface area which is structurally altered is limited to ~ 0.01 mum^2 per track. Kelvin probe force microscopy reveals that those surface tracks consist of electronically modified material and that a few tracks suffice to shift the surface potential of the whole single layer flake by ~ 400 meV. Thus, the irradiation turns the initially n-doped graphene into p-doped graphene with a hole density of 8.5 x 10^{12} holes/cm^2. This doping effect persists even after heating the irradiated samples to 500{\deg}C. Therefore, this charge transfer is not due to adsorbates but must instead be attributed to implanted atoms. The method presented here opens up a new way to efficiently manipulate the charge carrier concentration of graphene.