  A rotary nanomotor made of carbon nanostructures is introduced here. Through
a rotationally symmetrical layout of diamond wedges (or needles) outside of a
carbon nanotube and with the [100] direction of diamond along the tube's axial
direction, the wedge needle tips can drive the nanotube to rotate at gigahertz
frequency at room temperature. During thermal vibration, some of the atoms in
the nanotube collide with the needle tips. The tips provide the atoms with
continuous repulsion during collision. The tangential component of the
repulsion force produces a moment onto the nanotube about the tube axis.
Consequently, the nanotube is driven to rotate by the moment. The rotor reaches
stable rotation when the concentric outer tubes provide equivalent resistance
against the repulsion from needle tips. Molecular dynamics simulation results
indicate that the stability of the needle tips influences the rotational
frequency of the rotor. Potential fabrication of such a nanomotor is
illustrated with consideration of miniaturization. The rotary motor can act as
an engine in a nanomachine.
