  A gear effect is demonstrated at parallel and cross junctions between boron
nitride nanotubes (BNNTs) via atomistic simulations. The atoms of neighboring
BNNTs are meshed together at the junctions like gear teeth through long-range
non-covalent interaction, which are shown to be able to transmit motion and
power. The sliding motion of a BNNT can be spontaneously translated to rotating
motion of an adjoining one or viceversa at a well-defined speed ratio. The
transmittable motion and force strongly depend on the helical lattice structure
of BNNTs represented by a chiral angle. The motion transmission efficiency of
the parallel junctions increases up to a maximum for certain BNNTs depending on
displacement rates. It then decreases with increasing chiral angles. For cross
junctions, the angular motion transmission ratio increases with decreasing
chiral angles of the driven BNNTs, while the translational one exhibits the
opposite trend.
