Flipping nanoscale ripples of free-standing graphene using a scanning tunneling microscope tip

We present a scanning tunneling microscopy study of the stress-strain behavior of a rippled single-layer free-standing graphene (FSG) and report that FSG exhibits a non-linear sigmoidal stress-strain behavior. We managed to pull and push nanoripples by controlling the STM tip-FSG interaction forces. In this way, we found that the initial deformations of a rippled FSG involve sign reversals of the nanoripple's local curvatures, termed "flipping". In contrast to elastic deformation of graphene, flipping of a FSG nanoripple encounters a stress barrier and therefore makes a rippled FSG metastable, as evidenced by monitoring a yielding process in both experiments and molecular dynamics simulations. The evolution of nanoripples subjected to STM control is also fully consistent with atom-resolved images. Our work therefore shows how rippled 2D carbon deforms at nanoscale.