Molecule and cluster bombardment: Energy loss, trajectories, and collision cascades

The penetration of energetic molecules and clusters through solid material and associated radiation effects may be looked at as the sum of events induced by independent atoms. This picture is often adequate as a first approximation but it has definite limitations. The present paper reviews physical effects which cause more or less drastic modifications of this first-order picture. A number of sources of nonlinearities and correlations are identified. The emphasis is laid on stopping, multiple scattering, and collision-cascade kinematics. The discussion is mostly qualitative and based more on intuitive arguments and a few experimental results than on quantitative models.