Anisotropic straining of graphene using micropatterned SiN membranes

We use micro-Raman spectroscopy to study strain in free-standing graphene monolayers anchored to SiN holes of non-circular geometry. We show that a uniform differential pressure load yields measurable deviations from hydrostatic strain, conventionally observed in radially symmetric microbubbles. A pressure load of 1 bar yields a top hydrostatic strain of ≈ 0.7% and a G± splitting of 10 cm-1 in graphene clamped to elliptical boundaries with axes 40 and 20 μm, in good agreement with the calculated anisotropy Δϵ ≈ 0.6% and consistently with recent reports on Grüneisen parameters. The implementation of arbitrary strain configurations by designing suitable boundary clamping conditions is discussed.