Scanning Kelvin microscopy as a tool for visualization of optically induced molecular switching in azobenzene self assembling films

Scanning Kelvin microscopy (SKM) is applied to investigate the optically in duced cis-hans isomerization of self-assembled monolayers of azobenzene con taining thiols, Using a microcontact printing technique an array of circula r dots of dodecanethiol with a diameter of similar to 10 mu m is first self -assembled on a gold surface, The surrounding uncovered gold surface is sub sequently immersed in a solution of 4-fluoro-methyl-4-(10-mercaptodecyl-oxy )azobenzene, yielding a self-assembled monolayer on the uncovered gold area s. These two materials have dipole moments that differ in their vertical co mponent. The resulting local differences in the surface potential can be de tected clearly with the SKM, The optically induced cis-trans isomerization of the azobenzene results in a local change of the surface potential that a lso can be detected with the SKM, Illuminating the sample with light modula tes the amplitude of the surface potential signal detected over the azobenz ene-covered areas. It is possible to observe in situ the optical switching of these molecules with a spatial resolution in the micron range. Copyright (C) 2000 John Wiley & Sons, Ltd.