  We have calculated the momentum distributions of nanoparticles in diffraction
and interference dependent on the effective screening mass parameter or size
parameter and presented the calculations for a nanoparticle inside an infinite
square potential well and for a tunnelling nanoparticle through a square
potential barrier. These results display the transition from quantum to
classical mechanics and the simultaneous wave-particle duality of
nanoparticles. The concept that the effective screening effect increases with
increasing size of an object paves way for development of nanomechanics and
nanotechnology.
