Controlled growth of organic nanofibers on nano- and micro- structured gold surfaces Morten Madsen * , Roana Melina de Oliveira Hansen, Jakob Kjelstrup-Hansen, Horst-Günter Rubahn NanoSYD, Mads Clausen Institute, University of Southern Denmark, Alsion 2, DK-6400, Sønderborg, Denmark ABSTRACT Nanofibers made from para-hexaphenylene (p6P) molecules hold unique optoelectronic properties, which make them interesting candidates as elements in electronic and optoelectronic devices. Typically these nanofibers are grown on specific single-crystalline substrates, on which long, mutually parallel nanofibers are formed. However, the lack of ability to further process these substrates restrains their use in devices. In this work, a novel method for in-situ growth of p6P nanofibers on nano- and micro-structured gold surfaces is presented. The substrates are prepared by conventional microfabrication techniques such as lithography, etching and metal deposition, which increase their potential as device platforms. The results presented here demonstrate, that both the growth direction and the nanofiber length can be controlled by placement of nano- and micro-structured lines on the substrate. It is shown that the preferred growth direction of the nanofibers is perpendicular to these structures whereas their length scales are limited by the size and placement of the structures. This work therefore demonstrates a new technique, which can be useful within future organic nanofiber based applications. Keywords: Organic semiconductors, organic nanofibers, in-situ growth, nanofiber integration 1. INTRODUCTION Much attention is devoted to organic semiconductors due to their interesting optoelectronic properties, relative ease of processing, and price. Although such materials cannot compete with silicon-based electronics in terms of switching speed, organic transistors are very competitive for large area applications and for use with flexible substrates. 1 In addition, organic semiconductors with direct bandgap are suitable for optoelectronic applications such as organic light- emitting diodes (OLEDs) 2 and solar cells. 3 Typically, these materials are prepared in the form of an amorphous film for example by spin coating. However, using appropriate deposition techniques, a certain type of phenylene-based molecules can self-assemble in a crystal structure. At the same time, the self-assembly process causes the molecules to form nanoscale, elongated structures – ‘nanofibers’ on specific growth substrates. For example, para-hexaphenylene (p6P) molecules can form blue light emitting nanofibers with a wide range of useful optical properties 4 such as intense, anisotropic luminescence, waveguiding, and lasing. Typically, these nanofibers are grown by physical vapor deposition of the molecules on muscovite mica, on which mutually parallel nanofibers are formed. However, for device applications mica is not suitable, since further processing is impractical. Today, several techniques for transferring nanofibers or nanowires from growth substrates to device substrates have been demonstrated. Especially in the case of inorganic nanowires, techniques for transferring ensembles of nanowires have been demonstrated for example by contact printing, 5, 6 roll printing, 7 or by fluidic integration. 8 For the more fragile, organic nanofibers, transfer techniques have also been developed, 9 however, transferring of mutually parallel nanofibers onto specific micrometer sized regions, which is often needed for device applications, is a very difficult and time-consuming task. * madsen@mci.sdu.dk Nanoepitaxy: Homo- and Heterogeneous Synthesis, Characterization, and Device Integration of Nanomaterials, edited by M. Saif Islam, A. Alec Talin, Stephen D. Hersee, Proc. of SPIE Vol. 7406, 74060R · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.825281 Proc. of SPIE Vol. 7406 74060R-1 Downloaded from SPIE Digital Library on 02 Nov 2010 to 130.226.87.178. Terms of Use: http://spiedl.org/terms