The characterization of polycrystalline materials using ISS

Abstract

Some use has been made of low energy ion scattering from single crystals to determine surface crystallography and composition. Descriptions of these applications are given elsewhere in this volume. The ISS method also shows considerable promise for polycrystalline materials whose surfaces are frequently much different from the bulk composition. Engineering materials are often contaminated by impurities, processing aids, and bulk alloying constituents which have segregated at the surface. Low energy ISS allows first monolayer sensitivity not possible with methods such as AES and XPS where analysis is obtained over an average depth governed by penetration and excitation phenomena. Low energy ion scattering also provides minimum destruction to sensitive surfaces whose stoichiometry may be altered by electron stimulated desorption or knock-on effects of high energy ion bombardment. An example of such a surface is the failure surface at a weak boundary layer containing fluorine. Serious quantitation problems exist, caused by uncertain geometric and neutralization effects, but sensitivity factors do not vary to the extent of some other techniques such as SIMS. This paper reviews experimental aspects, advantages, limitations and applications of low energy ion scattering for the surface characterization of polycrystalline materials. Recent and future developments are briefly discussed.