Patterning 2D Metallic Surfaces by Soft Lithography
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Patterning 2D Metallic Surfaces by Soft Lithography M. Toprak, D. K. Kim, M. Mikhailova, M. Muhammed Materials Chemistry Division, Royal Institute of Technology, SE-100 44 Stockholm, Sweden ABSTRACT In this study, we report on the development of a µCP technique, where the ink used on the surface of the stamp is made of aminopropyl trimethoxy silane (APTMS). The stamps for the µCP are prepared by polymerizing polydimethylsiloxane (PDMS) on photolithographically defined masters. Si wafers were used as the substrate on which a self assembled layer of APTMS was formed at the contact regions of the stamp. The regions of contact were subsequently used for the deposition of gold coated magnetite nanoparticles, resulting in 2D patterned metallic surfaces. The colloidal particles were analyzed by TEM and XRD, and the printed substrates were characterized by AFM. INTRODUCTION The fabrication of large areas of structured surfaces with feature sizes in the nanometer regime is still a challenge. Modern approaches for constructing surfaces in the sub-micrometer range involve the use of lithographic techniques. Microcontact printing (µCP) is a non-photolitographic technique for generating patterned, self-assembled monolayers (SAMs) on the surface of a variety of substrates, such as gold, silver, copper and silicon dioxide [1-4]. µCP is a versatile and powerful technique to create chemical and biological patterns on substrates. Structures constructed by imprinting methods show impressive variability in shape and order. µCP employs an inked patterned stamp to direct chemical reactions between molecules from the ink and the surface of a substrate. Because of its simplicity, µCP has been widely adopted to form chemical patterns on both planar and non-planar surfaces. This technique has been conveniently used to form chemical patterns of alkylthiol and, trichloro silane monolayers on Au substrates. These monolayers provide good protection of the Au substrate against etchants and are mainly used as nanometer thick resists in selective chemical etching of the underlying substrates. The reverse process, i.e. the assembly of colloidal metal particles onto a specially terminated organic surface, has been achieved through specific interactions between the metal nanoparticles and the surface terminating groups, e.g. -NH2 and -SH. A two dimensional array of Au nanoparticles have been prepared by using this technique [5,6]. In this respect, patterning of SAMs attracts considerable interest. Fabrication of colloidal gold micro-patterns has been reported using a photolitographed, self assembled monolayer of mercaptopropyl silane on SiO2 substrates [7]. Copper patterns with feature sizes up to 1 µm have been formed by lithographically patterning an aminosilane film on diamond using UV radiation and a contact mask prior to catalyst deposition and copper CVD [8]. Inorganic catalysts have also been deposited on substrates for subsequent metallization of Cu on patterned surfaces [9]. Nanostructured magnetite films have been studied due to their unique
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