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

Functionalized alkanethiols offer tremendous flexibility in customizing the physicochemical properties of Au surfaces. For this reason they are being investigated for applications in sensing, tribology, and corrosion inhibition. We present a scanning tunneling microscopy characterization of molecular ordering in an alkanethiol monolayer system. When 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 homogeneous nucleation and grows into a complex domain network. Simultaneously, the pit number density and size distribution are observed to evolve in a manner consistent with Ostwald ripening. The number density of pit features follows a t(-1/2) power law. When the monolayer has completely crystallized, the redistribution of Au atoms ceases. Thus, this is a special case of order-disorder-mediated Ostwald ripening.