Probing thermal expansion coefficients of monolayers using surface enhanced Raman scattering

Abstract

Monolayer transition metal dichalcogenides exhibit remarkable electronic and optical properties, making them candidates for application within flexible nano-optoelectronics, however direct experimental determination of their thermal expansion coefficients (TECs) is difficult. Here, we propose a non-destructive method to probe the TECs of monolayer materials using surface-enhanced Raman spectroscopy (SERS). A strongly coupled Ag nanoparticle over-layer is used to controllably introduce temperature dependent strain in monolayers. Changes in the first-order temperature coefficient of the Raman shift, produced by TEC mismatch, can be used to estimate relative expansion coefficient of the monolayer. As a demonstration, the linear TEC of monolayer WS₂ is probed and is found to be 10.3 × 10⁻⁶ K⁻¹, which would appear support theoretical predictions of a small TEC. This method opens a route to probe and control the TECs of monolayer materials.