All-Optical Blister Test of Suspended Graphene Using Micro-Raman Spectroscopy

TL;DR

This study uses micro-Raman spectroscopy to non-invasively measure the mechanical properties of suspended graphene membranes under pressure, enabling precise determination of Young's modulus and strain effects.

Contribution

It introduces an all-optical, contactless method to analyze the mechanical response of graphene membranes, validating theoretical pressure scaling and measuring Grüneisen parameters.

Findings

Young's modulus of graphene measured as 1.05 TPa

Blister height scales with pressure to the one-third power

Grüneisen parameters for G and 2D modes determined

Abstract

We report a comprehensive micro-Raman study of a pressurized suspended graphene membrane that hermetically seals a circular pit, etched in a Si/SiO$_2$ substrate. Placing the sample under a uniform pressure load results in bulging of the graphene membrane and subsequent softening of the main Raman features, due to tensile strain. In such a microcavity, the intensity of the Raman features depends very sensitively on the distance between the graphene membrane and the Si substrate, which acts as the bottom mirror of the cavity. Thus, a spatially resolved analysis of the intensity of the G- and 2D-mode features as a function of the pressure load permits a direct reconstruction of the blister profile. An average strain is then deduced at each pressure load, and Gr\"{u}neisen parameters of $1.8\pm0.2$ and $2.4\pm0.2$ are determined for the Raman G and 2D modes, respectively. In addition, the measured blister height is proportional to the cubic root of the pressure load, as predicted theoretically. The validation of this scaling provides a direct and accurate determination the Young's modulus of graphene with a purely optical, hence contactless and minimally invasive, approach. We find a Young's modulus of $(1.05\pm 0.10) \rm TPa$ for monolayer graphene, in a perfect match with previous nanoindentation measurements. This all-optical methodology opens avenues for pressure sensing using graphene and could readily be adapted to other emerging two-dimensional materials and nanoresonators.