  Graphene grown by chemical vapour deposition is transferred on top of flat
gold nanoislands and characterized by scanning tunnelling microscopy (STM) and
atomic force microscopy (AFM). Graphene bubbles are formed with lateral
dimensions determined by the size and shape of nanoislands. These graphene
bubbles can be squeezed during STM imaging using bias voltages of less than 250
mV and tunnelling currents of 1 nA. Similarly, the graphene suspended over gold
nanovoids is deflected 4 - 5 nm by the STM tip when imaging at low bias
voltages (U = 30 mV). Nanoindentation measurements performed by AFM show that
the squeezing of graphene bubbles occurs at repulsive forces of 20 - 35 nN, and
such forces can result in deflections of several nanometres in suspended
graphene parts, respectively. Comparing the AFM and STM results, this study
reveals that mechanical forces of the order of 10e-8 N occur between the STM
tip and graphene under ambient imaging conditions and typical tunnelling
parameters.
