STRUCTURAL OBSERVATION OF CDST(2) LB FILMS AND NANOMETER-SCALE LITHOGRAPHY BY ATOMIC-FORCE MICROSCOPY

Langmuir-Blodgett (LB) films and related thin organic films have been the objects of increasing technological and scientific interest over the past 20 years. Optimization of the macroscopic physical properties of these systems requires a detailed understanding of their structure-property relations on microscopic scale, including the structure of transferred LB films on solid substrates, the nucleation of crystalline phase and their phase transitions. At the air-water interface the phase states of lipid monolayers and their transitions have been investigated by fluorescence and Brewster microscopy. Similar studies on transferred LB films at the air-substrate interface, however, have rarely been reported. On the other hand, fluorescence microscopy is limited to structure larger than 1 mu m in diameter. The atomic force microscope (AFM), which was recently used to study the surface structure of LB films, has the advantage of probing only the surface topography and the capability to resolve individual molecules([1,2]). Moreover, in some cases the AFM data revealed previously defect structures at molecular resolution([3,4]) and inhomogeneities in ordered surfaces of LB films. In this study, we applied AFM to investigate the surface structures of cadmium stearate (CdSt(2)) LB films transferred onto solid supports, ranging from morphology on the micrometer scale down to intermolecular spacing on the angstrom scale. Intrinsic defects in the LB monolayer have been used to measure the film thickness, and the lattice structure of CdSt(2) molecules was clearly observed. Experimental results indicate that the surface structure of the substrate strongly modulate the phase of deposited molecules and the integrity of LB films. Furthermore, by increasing the applied force on the AFM tip, we can manipulate LB films on nanometer scale.