JAIN ET AL. VOL. 6 ’ NO. 5 ’ 3861–3867 ’ 2012 www.acsnano.org 3861 April 11, 2012 C 2012 American Chemical Society Aligned Growth of Gold Nanorods in PMMA Channels: Parallel Preparation of Nanogaps Titoo Jain, † Samuel Lara-Avila, ‡ Yann-Vai Kervennic, ‡ Kasper Moth-Poulsen, § Kasper Nørgaard, † Sergey Kubatkin, ‡, * and Thomas Bjørnholm †, * † Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen Ø, Denmark, and ‡ Department of Microtechnology and Nanoscience and § Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 9, S-41296 Gothenburg, Sweden T he fabrication of metallic electro- de pairs separated by a few nano- meters is a fundamental challenge in nanotechnology and is well beyond the capabilities of current microfabrication tech- niques. 1 Possible areas of application lie within, for example, single-molecule electro- nics, 2 spectroscopy, 3 and plasmonics. 4 Thus far, top-down approaches such as the mechanical controllable break junction, 5,6 shadow mask evaporation, 7 and electro- migration 8,9 have proven successful in fab- ricating nanoelectrodes. Common shortcom- ings of these techniques are time consump- tion, low throughput, and the requirement for expensive and complicated experimen- tal setups normally operating at cryogenic temperatures. 10 In contrast, bottom-up approaches for the fabrication of nanogap devices are cur- rently much less explored, despite their potential for being more cost-effective and providing parallel fabrication routes for the production of multiple devices in only a few synthetic steps. 11À14 Efforts in this direction have typically focused on the integration of (bottom-up) prepared nanoparticles into devices, where precise control of placement is required. 15À18 Gold nanorods (AuNRs) have received considerable attention due to their facile synthesis and interesting physical proper- ties, many of which originate from their anisotropic nature. Using a variety of meth- ods, AuNRs have been self-assembled in one, 19,20 two, 21 and three 22 dimensions. Directional assembly of AuNRs has been obtained via electric field-assisted deposi- tion between lithographically defined elec- trodes, 23 using carbon nanotubes as templates, 24 stretching AuNR-embedded poly(vinyl alcohol) polymer films, 25,26 and employing capillary forces in polymer guid- ing templates. 27,28 Similar strategies have been employed for ∼5 μm long gold nano- wires over large areas, 29 and nanowires of different materials have been assembled using, for example, flow-induced align- ment, 30 while fabrication of carbon nano- tube arrays 31 has been demonstrated in scalable high-performance electronics. 32 Herein, we employ a combination of top- down and bottom-up approaches for the fabrication of nanogap junctions by direc- ted in situ growth of AuNR-based nano- structures inside prepatterned poly(methyl methacrylate) (PMMA) nanochannels on silicon dioxide surfaces. The effect of PMMA channel width on AuNR alignment * Address correspondence to sergey.kubatkin@chalmers.se, thob@adm.ku.dk. Received for review December 20, 2011 and accepted April 11, 2012. Published online 10.1021/nn204986y ABSTRACT We demonstrate alignment and positional control of gold nanorods grown in situ on substrates using a seed-mediated synthetic approach. Alignment control is obtained by directing the growth of spherical nanoparticle seeds into nanorods in well-defined poly(methyl methacrylate) nanochannels. Substrates with prepatterned metallic electrodes provide an additional handle for the position of the gold nanorods and yield nanometer-sized gaps between the electrode and nanorod. The presented approach is a novel demonstration of bottom-up device fabrication of multiple nanogap junctions on a single chip mediated via in situ growth of gold nanorods acting as nanoelectrodes. KEYWORDS: gold nanorods . nanoparticles . nanogaps . self-assembly . single-molecule electronics . nanoelectrodes . junctions ARTICLE