Tip Dependence of the Self-Assembly in Dip-Pen Nanolithography

Abstract

In dip-pen nanolithography (DPN), an atomic force microscopy tip delivers molecules to the substrate and generates a self-assembled monolayer (SAM) with a nanometer resolution. Given the tip changes from experiment to experiment, it is important to know how DPN is affected by the change in the tip. In principle, a change in the tip can alter the initial conditions and the subsequent dropping of molecules from the tip to the substrate. The present molecular dynamics simulation compares DPN results obtained from two different tips, a quill type spherical tip and a cylindrical tip like a fountain pen. We investigate how the nanodroplet created under the tip spreads out to form a SAM on a goldlike substrate. For the early stage of DPN studied here (less than 1.5 ns), we find that a substantial variation in the tip does not yield any significant change in DPN. For a strong molecular binding to the substrate in particular, a SAM is entirely determined by the molecule—substrate binding energy, not by the detailed geometry of the tip. The dynamic features of growth in the SAM are also similar for both tips.