Atomic force microscopy of instabilities and reorganization of Langmuir-Blodgett films

The atomic force microscope was used to show that Langmuir-Blodgett films are unstable to reorganization via a folding mechanism by which uniformly thick films spontaneously form holes and multilayer steps. These bilayer step defects originate at isolated sites and quickly spread to cover the entire film. The defects retain the sixfold symmetry of the underlying molecular lattice; after sufficient time, straight edges begin to form and the entire film is comprised of high islands with straight edges aligned with sixfold symmetry. The kinetics of the reorganization depend strongly on the chain length of the fatty acid used and the nature of the substrate. The results suggest that the reorganization is driven by an interconversion of strained, asymmetric monolayers to unstrained, centrosymmetric bilayers.