Irradiation of InP with MeV Se ions directed a few degrees off the sur
face normal leads to a lateral displacement of the implanted material.
Adjacent surface regions that are not irradiated remain unaffected. T
he dependence of the displacement on ion energy and its directionality
strongly suggest that the effect is caused by momentum transfer from
the ion to the solid. The amount of displaced material as a function o
f ion beam energy or angle of incidence can be described with a simple
model incorporating a shear stress, applied to the target as the ion
slows down, and radiation enhanced viscosity.