  We have reported the dependence of projectile mass, chemical reactivity and
effect of molecular beams on the ion induced nano structure formation, when 8
keV He1+, N1+, O1+, Ar1+ atomic ions and 16 keV N21+ and O21+ molecular ions
are bombarded on the Si(100) surface at an incidence angle of 60^{\circ}.
Atomic force microscopy (AFM) measurement shows that the initiation and growth
of ripple structures are determined not only by the collision cascades but also
by the chemical reactivity and molecular state of the projectiles. This
experimental investigation explores the necessary requirements for ion induced
controlled nanopatterning.
