Transport Mechanisms of Alkanethiols during Microcontact Printing on Gold

Microcontact printing (uCP) with elastometic stamps is a versatile method to modify the chemistry of surfaces. We explore this patterning process here, examining the origin and character of its limits, and demonstrating how best to use uCP and alkanethils for lithography on gold at submicron scales. We find that, ultimately, this type of lithography is constrained by the need to carry the monolayer-forming reaction to completion, with significant degradation of the accuracy of prints at sub-500-nm scales due to molecular diffusion. Printing monolayers of eicosanethiol on gold proved to be the best practical compromise between self-assembly of the resist and its transport along the stamp and substrate interfaces as well as through the gas phase. Results for this system were particularly sensitive to the geometry of the stamp and how eicosanethiol was placed on, and transferred from, its surface to the gold. Our experiments, and simulations that corroborate them, show the relative importance of the various paths in controlling the chemical contrast on the substrate. We demonstrate the fabrication of high-density arrays of approx. 90-nm gold dots using these criteria.