Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a SiO2 Substrate

TL;DR

This study investigates how structural distortions and environmental factors like oxygen and moisture influence hole doping in graphene on SiO2, revealing reversible and irreversible doping mechanisms linked to oxygen adsorption and substrate interactions.

Contribution

It uncovers the roles of substrate coupling and environmental exposure in controlling oxygen-induced hole doping in graphene, using Raman spectroscopy and microscopy.

Findings

Oxygen reversibly dopes graphene in dry conditions.

Moisture and prolonged exposure lead to more irreversible doping.

Structural distortion correlates with charge doping, not strain.

Abstract

Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO2 and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.