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/SiO2 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 ± 0.2 and 2.4 ± 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 ± 0.10) 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.

Raman spectroscopy of electrochemically gated graphene transistors: Geometrical capacitance, electron-phonon, electron-electron, and electron-defect scattering

“…81,82 From the data in Ref. 82, an intrinsic value corrected from interference effects of Table I), which is in excellent agreement with our estimate on suspended graphene.…”

“…Indeed, Γ G is marginally affected by isotropic strains below 1%. 82 However, the G-mode feature may broaden and ultimately split into two sub-features in the presence of larger anisotropic strains. 94,95 In addition, the Raman features soften (stiffen) under tensile (compressive) strain.…”

“…Finally, considering the Grüneisen parameters of 1.8 and 2.4 for the Raman G-and 2D-modes under isotropic strain, 82 we can estimate a slope of 7.1 × 10 −3 % strain/cm −1 to connect…”

“…A linear correlation between ω 2D and ω G has been measured in strained graphene. 78,82,[96][97][98] Since the measured slopes ( the correlation between ω 2D and ω G as a robust tool to optically separate strain from charge doping.…”

Colorimetry Technique for Scalable Characterization of Suspended Graphene

“…12,13 Single-layer graphene (SLG) drums have been extensively studied, showing unique mechanical properties. [14][15][16][17][18] Many groups have demonstrated the scalability of CVD SLG drums and analyzed the statistical variation of their mechanical properties by measuring several drums with laser interferometry, 19,20 Raman spectroscopy, 12,21,22 and atomic force microscopy. 23,24 However, any attempt to commercialize graphene mechanical sensors is ineffective unless a characterization technique that is parallel, contactless, and affordable at the same time becomes available.…”