Nanoscale molecular transport: The case of dip-pen nanolithography

In dip-pen nanolithography experiments, many groups have observed that different tips deliver the same ink at different rates. This article presents a quantitative model for understanding this phenomenon and, importantly, a way of controlling it. An inkjet printer is used to deliver controlled amounts of 16-mercaptohexadecanoic acid (MHA) to atomic force microscope tips in an array. Ink transport from each tip is studied as a function of the number of drops delivered. We show a nonlinear dependence of transport rates on the number of drops that arises from surface-area-dependent dissolution of MHA. From this work, MHA dissolution attempt frequencies were calculated to be between 1.3 x 109 and 4.4 x 109 Hz.