Nanotechnology 7 (1996) 452–457. Printed in the UK Microcontact printing of self-assembled monolayers: applications in microfabrication James L Wilbur, Amit Kumar, Hans A Biebuyck, Enoch Kim and George M Whitesides† Department of Chemistry, Harvard University, Cambridge, MA 02138, USA Abstract. This paper describes applications in microfabrication using patterned self-assembled monolayers (SAMs) formed by microcontact printing. Microcontact printing (μCP) is a flexible new technique that forms patterned SAMs with regions terminated by different chemical functionalities (and thus different physical and chemical properties), in patterns with μm dimensions. Patterns of SAM are formed using an alkanethiol as an ‘ink’, and printing the alkanethiol on a metal support with elastomeric ‘stamp’. We fabricate the stamp by moulding a silicone elastomer using a master prepared by optical or x-ray microlithography or by other techniques. SAMs of long-chain alkanethiolates on gold and other metals can act as nanometer resists by protecting the supporting metal from corrosion by appropriately formulated etchants: the fabrication of microstructures of gold and silicon demonstrates the utility of patterned SAMs (formed by μCP) as nm resists. Patterned SAMs formed by μCP can also control the wettability of a surface on the μm scale. The organization of liquids in patterned arrays with μm dimensions, and the patterned deposition of microcrystals and microcrystal arrays illustrate the use of controlled wettability for microfabrication. 1. Introduction Self-assembled monolayers (SAMs) of organic compounds on inorganic or metal surfaces are becoming increasingly important in many areas of materials science [1–3]. Although there are many different systems of SAMs based on different organic components and supports, the best developed systems are those of alkanethiolates, X(CH 2 ) n Y(CH 2 ) m S-, on gold films [4–6]. Alkanethiols chemisorb spontaneously on a gold surface from solution and form adsorbed alkanethiolates with loss of hydrogen. A wide variety of organic functional groups (X, Y ) can be incorporated into the surface or interior of the monolayer. SAMs can therefore be tailored to provide a wide variety of material properties: wettability and protection against corrosion by chemical etchants are especially relevant to many applications. We described previously [7–10] a technique that forms patterned SAMs with geometrically well defined regions of different chemical functionality and thus different physical and chemical properties. This technique, μCP, uses an elastomeric ‘stamp’ and alkanethiol ‘ink’ to form patterned SAMs of alkanethiolates on gold films with dimensions ranging from 200 nm to several cm. Patterned SAMs formed by μCP have many applications, including microfabrication [7, 8, 11–14], studies of wetting † Author to whom correspondence should be addressed. and nucleation phenomena [12, 15–19], protein [20, 21] and cellular adhesion [22]; and in analytical studies involving scanning electron microscopy [23], and scanning probe microscopies [24]. In this paper, we focus on applications related to the fabrication of structures with micrometer and sub-micrometer dimensions. 2. Results and discussion 2.1. Microcontact printing (μCP) transfers by contact alkanethiol ‘ink’ from an elastomeric ‘stamp’ to a gold surface: if the stamp is patterned, a patterned SAM forms [7, 8] The stamp is fabricated by casting polydimethylsiloxane (PDMS) on a master having the desired pattern. Masters are prepared using standard photolithographic techniques, or constructed from existing materials having microscale surface features. In a typical experimental procedure (figure 1), we placed a master in a glass or plastic petri dish, and poured a 10:1 ratio (w:w or v:v) mixture of SYLGARD silicone elastomer 184 and SYLGARD silicone elastomer 184 curing agent (Dow Corning Corporation) over the master. The elastomer degassed for approximately 30 min at room temperature, cured for 1–2 hr at 60 ◦ C, and was peeled gently from the master. The resulting stamp replicated 0957-4484/96/040452+06$19.50 c  1996 IOP Publishing Ltd