Optical Separation of Mechanical Strain from Charge Doping in Graphene

TL;DR

This paper introduces a method to optically distinguish and quantify mechanical strain and charge doping in graphene using Raman spectroscopy, facilitating better characterization of graphene-based materials and devices.

Contribution

The study demonstrates a correlation analysis technique that separates strain effects from charge doping in graphene's Raman spectra, overcoming previous interference issues.

Findings

Strain in graphene ranges from -0.2% to 0.4%.

Thermal treatments induce modest compression and hole doping.

Substrate-mediated strain is common in 2D materials.

Abstract

Graphene, due to its superior stretchability, exhibits rich structural deformation behaviors and its strain-engineering has proven useful in modifying its electronic and magnetic properties. Despite the strain-sensitivity of the Raman G and 2D modes, the optical characterization of the native strain in graphene on silica substrates has been hampered by excess charges interfering with both modes. Here we show that the effects of strain and charges can be optically separated from each other by correlation analysis of the two modes, enabling simple quantification of both. Graphene with in-plane strain randomly occurring between -0.2% and 0.4% undergoes modest compression (-0.3%) and significant hole doping upon thermal treatments. This study suggests that substrate-mediated mechanical strain is a ubiquitous phenomenon in two-dimensional materials. The proposed analysis will be of great use in characterizing graphene-based materials and devices.