Growth Dynamics of Self-Assembled Monolayers in Dip-Pen Nanolithography

Using molecular dynamics simulations, we studied the growth mechanism of self-assembled monolayers in dip-pen nanolithography. A molecule dropping from the tip kicks out a molecule sitting on the substrate, and the displaced molecule in turn kicks out a molecule next to it. This kicking propagates and finally stops when it hits the periphery of the monolayer. This monolayer growth is faster than predicted from the previous diffusion theory. Increasing the molecule−substrate binding strength enhances the molecular deposition rate and makes the monolayer well-ordered

Thermal Healing of a Mixed-Thiol Monolayer at the Nanoscale

Using molecular dynamics simulation, we study the thermal healing of a mixed-thiol monolayer grown by contact printing. By simulating the monolayers with various compositions of octadecanethiol and decanethiol molecules, we show that a mixed-thiol monolayer grown by contact printing contains a significant portion of unbound molecules which fail to bind their sulfur atoms to the underlying gold surface. A subsequent thermal annealing (300–370 K) however removes the unbound thiol molecules and gives an ordered and compact monolayer. We uncover the molecular pathways behind the removal of the unbound molecules during thermal annealing

Thermal Healing of the Nanometer-Wide Lines of Self-Assembled Monolayer

The structural and thermal properties of the nanometer-wide lines of a self-assembled monolayer (SAM) were investigated using molecular dynamics simulations. When grown by contact printing, a linear SAM contained a significant portion (8%) of unbound molecules that are inverted among upright molecules. This paper proposes thermal annealing (300–400 K) as an efficient method to remove the unbound molecules and improve the quality of the linear SAM. The partial melting of the SAM during heating enabled the unbound molecules to flip and adsorb. With subsequent cooling, the linear SAM recovered its compact ordered structure. The molecular mechanisms and activation energies involved in the thermal annealing were elucidated