Near field optical investigations of Langmuir-Blodgett monolayers in liquid environment

Langmuir-Blodgett monolayers are studied using near field fluorescence micr oscopy. The setup is equipped with a feed back system based on shear force detection of the oscillating near field probe that allows optical character ization in air as well as in aqueous environments. In the monolayer liquid condensed star-shaped domains are present in a fluorophore-doped liquid exp anded phase. The boundary lines between the two phases show a width of 91 n m. Observations in water give the same quality of the optical data and allo w the measurement of the boundary line width with the same optical resoluti on. The height data at constant amplitude of the probe vibration revealed t opographical contrast inversion when scanning over the boundary lines of th e monolayer in water with respect to scanning in air. This setup is suited to study optical properties of complex biological systems in an aqueous env ironment.