Interplay between Raman shift and thermal expansion in graphene: temperature-dependent measurements and analysis of substrate corrections

TL;DR

This study uses temperature-dependent Raman measurements of graphene on silicon nitride to clarify the sign and behavior of its thermal expansion coefficient, highlighting the importance of substrate corrections and many-body potential models.

Contribution

It provides experimental data and analysis showing that the graphene TEC is likely positive above room temperature, challenging previous quasiharmonic approximation calculations.

Findings

Graphene's TEC is likely positive above room temperature.

Many-body potential models accurately reproduce experimental data.

Substrate correction is crucial for interpreting Raman measurements.

Abstract

Measurements and calculations have shown significant disagreement regarding the sign and variations of the thermal expansion coefficient (TEC) of graphene $\alpha(T)$. Here we report dedicated Raman scattering experiments conducted for graphene monolayers deposited on silicon nitride substrates and over the broad temperature range 150--900~K. The relation between those measurements for the G band and the graphene TEC, which involves correcting the measured signal for the mismatch contribution of the substrate, is analyzed based on various theoretical candidates for $\alpha(T)$. Contrary to calculations in the quasiharmonic approximation, a many-body potential reparametrized for graphene correctly reproduces experimental data. These results indicate that the TEC is more likely to be positive above room temperature.