Ellipsoid-like structures formed by atomic force microscopy in Langmuir-Blodgett films of PMMA

The surface structure of Langmuir-Blodgett (LB) and cast films of poly(methyl methacrylate) (PMMA) in isotactic, syndiotactic and atactic conformations were probed by atomic force microscopy. The LB films exhibited smooth surfaces during the first scan, but as scanning continued ellipsoid-like structures developed with the long axes oriented parallel to the scanning direction of the tip. The average size of the ellipsoids in the XY plane was about 100 nm × 60 nm for isotactic PMMA films, but considerably smaller for syndiotactic and atactic samples, and a few nanometers in the Z direction. In contrast, the surfaces of the cast films showed images which were very stable to scanning. The surfaces of both LB and cast films exhibited no period structure. The formation of ellipsoid-like structures in LB film surfaces during scanning can be attributed to the transition of extended chain conformations to random coils