  The lifting, peeling and exfoliation of physisorbed ribbons (or flakes) of 2D
material such as graphene off a solid surface are common and important
manoeuvres in nanoscience. The feature that makes this case peculiar is the
structural lubricity generally realized by stiff 2D material contacts. We model
theoretically the mechanical peeling of a nanoribbon of graphene as realized by
the tip-forced lifting of one of its extremes off a flat crystal surface. The
evolution of shape, energy, local curvature and body advancement are ideally
expected to follow a succession of regimes: (A) initial prying, (B) peeling
with stretching but without sliding (stripping), (C) peeling with sliding, (D)
liftoff. In the case where in addition the substrate surface corrugation is
small or negligible, then (B) disappears, and we find that the (A)-(C)
transition becomes universal, analytical and sharp, determined by the interplay
between bending rigidity and adsorption energy. This general two-stage peeling
transition is identified as a sharp crossover in published data of graphene
nanoribbons pulled off an atomic-scale Au(111) substrate.
