Analysis of Langmuir-Blodgett overlayers by time-of-flight secondary ion mass spectrometry (TOF-SIMS)

High-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS) in combination with ion imaging (lateral resolution 1 mu m) has been applied to the analysis and characterization of thin organic films prepared by the Langmuir-Blodgett (LB) technique. Films made from monomeric (stearic acid) as well as polymeric amphiphiles (modified polymethacrylate, modified polyamide) were investigated and compared. Noble metals (Ag, Au) evaporated onto polycarbonate slices were used as substrate materials. Whereas ion imaging of LB films made from stearic acid reveals defect structures of a diameter of less than 1 mu m, the polymeric amphiphiles have been found to form homogeneous and closed layer structures. The sampling depths of secondary ions are strongly related to the structure of the LB films. For the polymeric amphiphiles the sampling depths are smaller than three monolayers (6 nm). Binary mixtures consisting of monomeric species in a polymeric matrix show a vertical diffusion of the monomeric component towards the surface. More application oriented investigations have included the detection and localization of contaminations, the investigation of the long term behaviour of LB systems, and the investigation of the stability against higher temperatures and contact with solvents.