Tip-enhanced Raman mapping of local strain in graphene

We demonstrate local strain measurements in graphene by using tip-enhanced Raman spectroscopy (TERS). We find that a single 5 nm particle can induce a radial strain over a lateral distance of ∼170 nm. By treating the particle as a point force on a circular membrane, we find that the strain in the radial direction (r) is ∝ r−(2 3),in agreement with force-displacement measurements conducted on suspended graphene flakes. Our results demonstrate that TERS can be used to map out static strain fields at the nanoscale, which are inaccessible using force-displacement techniques.