Development of Knife-Edge Ridges on Ion-Bombarded Surfaces
  We demonstrate in both laboratory and numerical experiments that ion bombardment of a modestly sloped surface can create knife-edge like ridges with extremely high slopes. Small pre-fabricated pits expand under ion bombardment, and the collision of two such pits creates knife-edge ridges. Both laboratory and numerical experiments show that the pit propagation speed and the precise shape of the knife edge ridges are universal, independent of initial conditions, as has been predicted theoretically. These observations suggest a novel method of fabrication in which a surface is pre-patterned so that it dynamically evolves to a desired target pattern made of knife-edge ridges. 
Miranda Holmes-Cerfon, Wei Zhou, Andrea L. Bertozzi, Michael P.   Brenner, and Michael J. Aziz
cond-mat.mtrl-sci