Study of Thermal Expansion Coefficients of 2D Materials via Raman Micro-spectroscopy: Revisited

TL;DR

This study combines Raman micro-spectroscopy and simulations to investigate how substrates influence the thermal expansion of supported 2D materials, revealing substrate effects on vibrational modes and TEC, with a new measurement scheme for supported graphene.

Contribution

It introduces a Raman-based method to measure the TEC of supported 2D materials and revisits the TEC of graphene considering substrate interactions.

Findings

Substrate significantly affects graphene's vibrational modes and TEC.

The TEC of supported graphene on OTS substrate is approximately -0.6×10^-6/K.

Supported graphene's TEC is smaller than that of free-standing graphene.

Abstract

We report a joint study, using Raman micro-spectroscopy and molecular dynamics simulations, on the substrate effect on thermal properties of 2D materials and revisit measurement of thermal expansion coefficient (TEC) of supported 2D film. Graphene is employed as a representative. We find that the out-of-plane coupling between graphene and substrate strongly affects the temperature-dependent vibrational modes and TEC of graphene. Density of states for long-wavelength out-of-plane oscillations is significantly reduced when graphene is supported on an alkane substrate. To account for the contribution of the out-of-plane coupling to TEC, a Raman micro-spectroscopic scheme is developed. The TEC of graphene on octadecyltrichlorosilane substrate is found to be (-0.6+-0.5)*10-6/K at room temperature, which is fundamentally smaller than that of free-standing graphene. Our results shed light on the understanding of the interaction between 2D material and substrate, and offer a general recipe for optical measurement of TEC of a supported 2D film.