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

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 Grüneisen parameters of $1.8\pm 0.2$ and $2.4\pm 0.2$ 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 $(1.05\pm 0.10)\mathrm{TPa}$ 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.

Manuscript File (11 pages, 7 figures) and Supplemental Material (6 pages, 9 figures)

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• Single pixel wide gamut dynamic color modulation based on graphene micromechanical system
• Protocol to perform pressurized blister tests on thin elastic films
• Single- and narrow-line photoluminescence in a boron nitride-supported MoSe${}_2$/graphene heterostructure