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

Abstract

Scanning Kelvin microscopy (SKM) is applied to investigate the optically induced cis–trans isomerization of self-assembled monolayers of azobenzene containing thiols. Using a microcontact printing technique an array of circular dots of dodecanethiol with a diameter of ∼10 µm is first self-assembled on a gold surface. The surrounding uncovered gold surface is subsequently immersed in a solution of 4-fluoro-methyl-4-(10-mercaptodecyl-oxy)azobenzene, yielding a self-assembled monolayer on the uncovered gold areas. These two materials have dipole moments that differ in their vertical component. The resulting local differences in the surface potential can be detected clearly with the SKM. The optically induced cis–trans isomerization of the azobenzene results in a local change of the surface potential that also can be detected with the SKM. Illuminating the sample with light modulates the amplitude of the surface potential signal detected over the azobenzene-covered areas. It is possible to observe in situ the optical switching of these molecules with a spatial resolution in the micron range. Copyright © 2000 John Wiley & Sons, Ltd.