Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges Ruben B. A. Sharpe, † Dirk Burdinski,* ,‡,§ Jurriaan Huskens,* ,†,⊥,# Harold J. W. Zandvliet,* ,†,∇ David N. Reinhoudt, †,# and Bene Poelsema †,∇ MESA+ Institute for Nanotechnology and Faculty of Science and Technology, UniVersity of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands, and Philips Research, High Tech Campus EindhoVen, 5656 AE EindhoVen, The Netherlands ReceiVed June 21, 2006. In Final Form: October 12, 2006 Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time. n-Octadecanethiol (ODT) was made to expand from the edges of 16-mercaptohexadecanoic acid (MHDA) monolayer patterns. Likewise, 11-mercaptoundecanol (MUD) was grown on MHDA and on ODT monolayer edges. The results of these experiments are in accordance with the moving boundary model for monolayer spreading. In addition to such surface-bound spreading, a vapor-phase contribution to lateral monolayer growth was identified. MUD was observed to be an excellent ink for creating chemical contrast by means of regioselective deposition from a vapor phase. As a proof of principle, ribbons of 11-mercaptoundecanol with submicrometer widths were grown on pentaerythritol-tetrakis(3-mercaptopropionate) edges, and submicrometer wide gold lines were produced by subsequent wet-chemical etching. Introduction The incessant demand for miniaturization in electronics, medical, and nanotechnology is currently met by the development of fabrication methods of ever-increasing complexity and cost. Soft-lithographic patterning techniques offer the potential for an alternative low-cost, large-area, and high-volume production technology. 1,2 Microcontact printing (μCP) is a particularly easy and versatile representative of the soft lithography family and has received a lot of attention in recent years. 2-4 In μCP self- assembled monolayers (SAMs) of amphiphilic nature, usually organic molecules are formed on the surface of a substrate only in the areas of contact with the ink-loaded soft lithography mask (stamp). With decreasing feature size, the mechanical stability of the utilized stamps becomes a limiting factor. 2,5-12 This challenge has to be met by materials that are by definition soft and flexible. An interesting novel approach to circumvent this problem is the creation of submicrometer patterns by using masks with micrometer-sized features, which are characterized by a higher mechanical stability and are therefore easier to produce and handle. Edge lithographic techniques utilize the edges of such large pattern features to determine submicrometer-sized structures. Examples include near-field phase-shifting photolithography, 13,14 topographically directed etching, 15,16 edge transfer lithography, 17 and controlled undercutting. 18 Because of their inherent mobility, the use of self-assembled alkanethiol monolayers in edge lithographic schemes would, in principle, allow for control of edge-feature sizes by controlling the process time. Edge-spreading lithography (ESL), an edge lithographic technique that exploits the propensity of alkanethiol SAMs for spreading, has recently been reported. 19,20 In this technique, the ink source (an inked rubber stamp) is decoupled from the substrate by freestanding structures on the substrate that act as physical guides for the spreading process. 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