  Understanding how the mechanical behavior of materials deviates at the
nanoscale from the macroscopically established concepts is a key challenge of
particular importance for graphene, given the complex interplay between its
nanoscale morphology and electronic properties. In this work, the (sub-)
nanometer wavelength periodic rippling of suspended graphene nanomembranes has
been realized by thermal strain-engineering and investigated using Scanning
Tunneling Microscopy. This allows us to explore the rippling of a crystalline
membrane with wavelengths comparable to its lattice constant. The observed
nanorippling mode violates the predictions of the continuum model, and
evidences the breakdown of the plate idealization of the graphene monolayer.
Nevertheless, microscopic simulations based on a quantum mechanical description
of the chemical binding accurately describe the observed rippling mode and
elucidate the origin of the continuum model breakdown. Spatially resolved
tunneling spectroscopy measurements indicate a substantial influence of the
nanoripples on the local electronic structure of graphene and reveal the
formation of one-dimensional electronic superlattices.
