  We report the observation of a novel phenomenon, the self-retracting motion
of graphite, in which tiny flakes of graphite, after being displaced to various
suspended positions from islands of highly orientated pyrolytic graphite,
retract back onto the islands under no external influences. Our repeated
probing and observing such flakes of various sizes indicate the existence of a
critical size of flakes, approximately 35 micrometer, above which the
self-retracting motion does not occur under the operation. This helps to
explain the fact that the self-retracting motion of graphite has not been
reported, because samples of natural graphite are typical larger than this
critical size. In fact, reports of this phenomenon have not been found in the
literature for single crystals of any kinds. A model that includes the static
and dynamic shear strengths, the van der Waals interaction force, and the edge
dangling bond interaction effect, was used to explain the observed phenomenon.
These findings may conduce to create nano-electromechanical systems with a wide
range of mechanical operating frequency from mega to giga hertzs.
