VELOCITY-DEPENDENT FORCES IN ATOMIC-FORCE MICROSCOPY IMAGING OF LIPIDFILMS

We have imaged adsorbed fluid lipid bilayers by atomic force microscop y. The patches were formed by rupture of phospholipid vesicles onto ma gnesium fluoride. We show that the membrane patches are fluid but can be stably imaged at scan rates higher than 6 mu m/s. At lower scan rat es the tip penetrates through the layer. The penetrating tip does not destroy the fluid patches, and the previous image can be restored afte r increasing the scanning velocity. The dynamic forces that possibly e xplain;the effect are discussed.