The photon emissions from excited Al atoms produced by different ion projectiles (e.g. He+, N+, Ne+, and Ar+) and projectile energies (10, 15, and 20 keV) bombarding single and polycrystalline Al targets were measured. The measured photon signals were analyzed by two different methods. The first one compares the measured photon yields and calculated nuclear stopping powers to each other. This comparison reveals that when both are a function of the reduced energy they have the same tendency. This result indicates that elastic collisions play the main role in producing the observed photon emissions. The other method analyzes the measured photon decay curves, as a function of the target moving distance in the consideration of the photon cascade effect. In the experiment we found that all the detected photon signals originated from fast moving sputtered particles. From the above observations, the production of sputtered and excited Al atoms can be referred to as a combination of the curve-crossing process and a binary-collision between the projectile and target atoms on or very near the target surface. When Ar+ and Ne+ ions bombarded an Al(111) target, this transformed the Al(111) into a polycrystalline Al target. Therefore, both targets under ion bombardment yield the same mean velocity of the sputtered particles and had the same photon cascade effect. (C) 1999 Elsevier Science B.V. All rights reserved.
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS