Anisotropic straining of graphene using micropatterned SiN membranes

TL;DR

This study demonstrates how micro-Raman spectroscopy can measure anisotropic strain in graphene suspended over micropatterned SiN membranes, revealing non-uniform strain profiles and their effects on vibrational properties.

Contribution

The paper introduces a method to induce and measure anisotropic strain in graphene using micropatterned SiN membranes with non-circular holes, expanding strain engineering capabilities.

Findings

Measured hydrostatic strain of ~0.7% at 1 bar pressure

Observed G-band splitting of 10 cm^{-1} due to anisotropic strain

Results align with recent Grüneisen parameter reports

Abstract

We use micro-Raman spectroscopy to study strain profiles in graphene monolayers suspended over SiN membranes micropatterned with holes of non-circular geometry. We show that a uniform differential pressure load $\Delta P$ over elliptical regions of free-standing graphene yields measurable deviations from hydrostatic strain conventionally observed in radially-symmetric microbubbles. The top hydrostatic strain $\bar{\varepsilon}$ we observe is estimated to be $\approx0.7\%$ for $\Delta P = 1\,{\rm bar}$ in graphene clamped to elliptical SiN holes with axis $40$ and $20\,{\rm \mu m}$. In the same configuration, we report a $G_\pm$ splitting of $10\,{\rm cm^{-1}}$ which is in good agreement with the calculated anisotropy $\Delta\varepsilon \approx 0.6\%$ for our device geometry. Our results are consistent with the most recent reports on the Gr\"uneisen parameters. Perspectives for the achievement of arbitrary strain configurations by designing suitable SiN holes and boundary clamping conditions are discussed.