Radiation damage during heavy ion elastic recoil detection analysis of insulating materials

Abstract

Loss of low- Z elements (H, C, N, O, etc.) during heavy ion Elastic Recoil Detection Analysis (ERDA) has been investigated for various molecular target materials, using beams of 79Br, 127I, 197Au and 209Bi at 1.1 MeV/amu. Ceramic targets such as Nb 2O 5 and UO 2 exhibit negligible oxygen loss even at fluences 100 times larger than that typically required during ERDA to determine the stoichiometry of a given material (10 12–10 13 ions/cm 2). However, silicon oxynitride targets and various organic materials (photoresist, polyethylene and polycarbonate films) exhibit observable losses of hydrogen, nitrogen, oxygen and even carbon in some cases. Thus ERDA of such materials requires small corrections to determine the original target composition. For all beams, the energy loss of the incident ion due to nuclear stopping is far too small to be responsible for the observed elemental depletion; hence the much larger electronic stopping must be the primary cause. In the silicon oxynitride and photoresist targets, the observed loss rates of H, C, N or O, normalised by the corresponding recoil cross section σ R, are roughly the same for all four beams. At a constant velocity of 1.1 MeV/amu, σ R depends approximately on Z 1 2 and the electronic energy loss is approximately proportional to Z 1. We therefore conclude that the depletion rate of low- Z elements also depends roughly on the square of the electronic energy loss.