MOLECULAR ORDERING AND GOLD MIGRATION OBSERVED IN BUTANETHIOL SELF-ASSEMBLED MONOLAYERS USING SCANNING-TUNNELING-MICROSCOPY

Functionalized alkanethiols offer tremendous flexibility in customizin g the physicochemical properties of Au surfaces. For this reason they are being investigated for applications in sensing, tribology, and cor rosion inhibition. We present a scanning tunneling microscopy characte rization of molecular ordering in an alkanethiol monolayer system. Whe n dense monolayers of butanethiol molecules are assembled onto Au(111) , randomly distributed single-layer-deep pit defects are generated in the Au substrate. The monolayer spontaneously crystallizes via homogen eous nucleation and grows into a complex domain network. Simultaneousl y, the pit number density and size distribution are observed to evolve in a manner consistent with Ostwald ripening. The number density of p it features follows a t(-1/2) power law. When the monolayer has comple tely crystallized, the redistribution of Au atoms ceases. Thus, this i s a special case of order-disorder-mediated Ostwald ripening.