Hysteretic responses of nanomechanical resonators based on crumpled few-layer graphene

The process of suspending two-dimensional materials over cavities etched in a substrate occasionally results in crumpled membranes. Their complicated morphologies feature an abundance of folds, creases, and wrinkles that make each crumpled membrane unique. Here, we prepare five nanomechanical resonators based on crumpled membranes of few-layer graphene and measure their static response and the resonant frequencies of their dynamic response. We tune both responses with a dc voltage applied between the membrane and an underlying gate electrode. Surprisingly, we find that all the resonators exhibit hysteretic responses as the gate voltage is increased and then decreased. Concomitant discontinuities in the static response and in the vibrational resonant frequencies indicate a sudden change in the shape and in the tensile strain of the membranes, accompanied by a change in elastic energy that we estimate. We find that the hystereses can be removed and regular responses can be restored by annealing the resonators.