Nanocontact Molding of Functional Photopolymer Resins for Direct Fabrication of Organic Electronics

Introduction Nanocontact molding and other related techniques of imprint lithography have received much attention as potentially simple and inexpensive tools for the accurate replication of sub-100 nm features. We have recently reported on the use of this method for the replication of features as a small as 60 nm. In this technique, an inexpensive mold is made by curing a photopolymer resin against a patterned silicon master written by ebeam lithography. This mold is then used to press into a photopolymer resin. The resin is then cured in contact with the mold, resulting in a highly reproducible positive copy of the original master pattern. The incorporation of embedded functionality into the photopolymer resin has allowed the utility of this technique to be advanced beyond that of simple pattern transfer. The inclusion of inimers (molecules containing both a dormant initiating site and a monomer functionality) allowed precise control of feature size and surface chemistry through modification of the surface after molding. One such inimer, a methacrylate monomer containing a dormant atom transfer radical polymerization (ATRP) initiator, allowed for the application of controlled free radical polymerization to grow polymer brushes from the surface of the molded features. The molecular weight of the brushes was controlled by the ratio of monomer to initiator and the resulting surface chemistry was decided by the choice of the monomer. Currently, we are interested in the adaptation of these techniques to functionalize patterned surfaces with conducting and semiconducting polymers for the direct fabrication of organic electronics. In earlier work, bromostyrene was embedded in the resin, and subsequently was used to iniate the Ni(0) mediated polymerization of 2,7-dibromo-9,9-dinonylfluorene resulting in a surface functionalized with short polyfluorene brushes. The current work focuses on the use of functional photpolymer resins for the attachment and growth of polythiophene brushes. Herein, we describe two methods for the functionalization of photopolymer reins with poly(3-hexyl2,5-thiophene). The materials and substrates were characterized by atomic force microscopy (AFM), ellipsometry, UV-vis spectroscopy, and fluorescence microscopy.