Molecular Dynamics of Monolayer Deposition Using a Nanometer Tip Source

Abstract

We performed a molecular dynamics simulation of the monolayer deposition from a nanoscale tip. We investigated how the nascent multilayer droplet around the tip spreads out to become a monolayer on the substrate eventually. A molecule on top pushes out a molecule below it, and the molecule just pushed out in turn pushes out a molecule next to it. The monolayer size grows when such a serial pushing propagates to its periphery. The monolayer periphery shows an initial diffusional growth in its time dependence followed by a slow subdiffusional expansion. We have examined the effects of molecule-substrate binding energy on the shape of the monolayer. For a relatively weak molecule−substrate binding, the monolayer is sparse and has irregular branches. As the molecule−substrate binding strengthens, the monolayer becomes compact and reflects the anisotropy of substrate. A substrate with a hexagonal symmetry results in a hexagonal and a starlike monolayer. An extremely strong molecule−substrate binding removes such an effect of the substrate anisotropy, giving rise to a circular monolayer. The monolayer growth rate exhibits a turn-over behavior with respect to the increase in the molecule−substrate binding strength.