STUDY OF LIQUID-CRYSTAL PREWETTING FILMS BY ATOMIC-FORCE MICROSCOPY IN TAPPING MODE

We demonstrate the use of tapping mode atomic force microscopy (TMAFM) for the study of liquid crystal prewetting films spreading on silicon wafers. With AFM, we are able to image the edge of the prewetting fil m when it spreads on the solid and to obtain images on its surface wit h a resolution in the nanometer range. As an example, we study the rou ghness of the film surface: we have observed, in agreement with theore tical predictions, that the undulations of the liquid films follow tho se of the solid surface (at least when the wavelength of the undulatio ns is large compared to the film thickness (similar to 5 NM)). Further , we show that when the drive amplitude or the set point is below a th reshold, a liquid crystal micromeniscus forms between the tip and the sample, causing an instability of the tip. Finally, we have also obser ved that the apparent thickness of the film depends on the imaging par ameters in a way that cannot be described by the models that are gener ally used to explain tapping mode operations.