Molecular-Scale Structures of Langmuir-Blodgett Films of Fatty Acids Observed by Atomic Force Microscopy

Abstract

Langmuir-Blodgett films of arachidic acid, barium arachidate, and a mixture of arachidic and behenic acids on a chemically flattened silicon substrate were observed by atomic force microscopy. The films were found to contact tightly with the substrate with a molecular slip at its steps. Lattice expansion due to barium ions was found on the barium arachidate film but not on the pure acid film. In addition, the 2×2 superlattice was found on the barium arachidate film. The superlattice structure may be caused by the formation of a hydrogen salt. Although no phase separation was found on the film made of a 9:1 mixture of the acids, the image of the expected molecular mixture has not been obtained so far.