Characterization of the surface layer of LB-films using a slow positron beam

Langmuir-Blodgett films were studied using a variable energy slow-positron beam. We measured the energy spectra of positron annihilation radiation for Cd and Mg eicosanoid films and obtained the V- and S-parameters as a funct ion of the incident positron energy, E. In the V-E curves of Cd eicosanoid films, there were dips at the positron energy whose mean implantation depth corresponding to the first and second Cd2+ layers from the surface. These dips are interpreted as the result of inhibition of Ps formation by the Cd2 + ions. The S-parameter was found to be sensitive to chemical composition o f the film and also to possible structural change due to heat treatment. Ou r results suggest that positron beams provide valuable information about th e microstructure of the Langmuir-Biodgett films. (C) 2000 Elsevier Science Ltd. All rights reserved.