Microcontact printing using a flat metal-embedded stamp fabricated using a dry peel-off process† Ikjoo Byun, a Anthony W. Coleman b and Beomjoon Kim * a A microcontact printing method using a flat metal-embedded poly- dimethylsiloxane (PDMS) stamp has been demonstrated. Metal patterns embedded in the PDMS stamp act as a molecular transport barrier. The flat stamp avoids the mechanical deformation of the stamp tip which is a crucial problem when printing the stamp onto a substrate. Microcontact printing (mCP) has rapidly developed into a robust printing tool for micro- or nano-fabrication over the past few decades. 1 It has triggered enormous interest from the surface science community, as well as from engineers and biologists. 2 Many applications that use this simple “stamping” process have been reported such as printing microelectrode arrays 3 or organic semiconductors. 4 Moreover, biological molecules, such as proteins, can be printed directly by stamping. 5 Also, Spatially- controlled cell growth (i.e. cellular micro-patterns) can be achieved by patterning specic cell adhesion molecules such as the RGD peptide 6 onto surfaces, which can also be used in association with patterns of protein-repellent PEG molecules. 7 Although mCP has several advantages compared to conven- tional lithography, an obvious limitation to mCP is the material properties of an elastomer. A polydimethylsiloxane (PDMS, typically Sylgard 184 from Dow Corning, Young's modulus 1.8 MPa (ref. 8)) is the most widely employed stamp material for mCP because its exibility allows excellent contact between the stamp and the substrate. Because the height of the stamp tip is commonly xed to several micrometers, stamp tips with different linewidths should have different aspect ratios. When the aspect ratio is too high or too low, PDMS structures tend to buckle, merge, laterally collapse, or roof collapse (Fig. 1A). 9 These are inevitable problems with a conventional PDMS stamp. Among several strategies to improve the resolution of mCP, one has been explored that changing the stamp materials from PDMS to a polymer with a higher Young's modulus to prevent mechanical collapse of the stamps. 10–12 Another method for preventing mechanical deformation of the stamp is to use a at PDMS stamp instead of a PDMS stamp with a physical structure. The key of at stamps is that self-assembled monolayer (SAM) inks are selectively soaked into the area dened by UV, 13 chemicals using nano-imprint lithography, 14 metal mask, 15 or dip-pen lithography. 16 Recently, mCP using a metallic stencil mask has been reported. 17 However, the PDMS stamp risks being contaminated by a metal etchant during the fabrication process. These approaches have solved the problems of mechanical deformation of conventional PDMS stamps, so that improved the resolution of the printing of individual features signicantly (down to approximately 50 nm). However, most of them are restricted by short lifetime, small pattern area, longer Fig. 1 Idealized illustration of (A) mCP failure by mechanical deformation of a conventional PDMS stamp, (B) mCP using a flat metal-embedded PDMS stamp, (C–F) mCP process using a flat metal-embedded PDMS stamp. a CIRMM, Institute of Industrial Science, The University of Tokyo, Tokyo, 153-8505, Japan. E-mail: bjoonkim@iis.u-tokyo.ac.jp b LMI-UMR 5615, CNRS, Universite Claude Bernard Lyon 1, 69622 Villeurbanne, France † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra44072a Cite this: DOI: 10.1039/c3ra44072a Received 1st August 2013 Accepted 17th October 2013 DOI: 10.1039/c3ra44072a www.rsc.org/advances This journal is ª The Royal Society of Chemistry 2013 RSC Adv. RSC Advances COMMUNICATION Published on 17 October 2013. Downloaded by Tokyo Daigaku on 30/10/2013 06:43:07. View Article Online View Journal