  Atomically thin boron nitride (BN) nanosheets are important two-dimensional
nanomaterials with many unique properties distinct from those of graphene, but
the investigation of their mechanical properties still greatly lacks. Here we
report that high-quality single-crystalline mono- and few-layer BN nanosheets
are one of the strongest electrically insulating materials. More intriguingly,
few-layer BN shows mechanical behaviors quite different from those of few-layer
graphene under indentation. In striking contrast to graphene, whose strength
decreases by more than 30% when the number of layers increases from 1 to 8, the
mechanical strength of BN nanosheets is not sensitive to increasing thickness.
We attribute this difference to the distinct interlayer interactions and hence
sliding tendencies in these two materials under indentation. The significantly
better mechanical integrity of BN nanosheets makes them a more attractive
candidate than graphene for several applications, e.g. as mechanical
reinforcements.

Materials Science