Formation of gold nanoparticles in polymeric nanowires by low-temperature thermolysis of gold mesitylene† Christoph Erk, a Man Yan Eric Yau, b Holger Lange, c Christian Thomsen, c Paul Miclea, de Ralf B. Wehrspohn, de Sabine Schlecht * a and Martin Steinhart * f Received 26th August 2011, Accepted 19th October 2011 DOI: 10.1039/c1jm14193g The formation of polymer nanowires containing metal nanoparticle chains by low-temperature thermolyses of metal precursors has remained challenging. We report the block copolymer-assisted generation of locally regular chains of quasi-spherical gold nanoparticles with narrow particle diameter distribution by mild thermolysis of the non-polar gold precursor gold mesitylene inside the cylindrical nanopores of self-ordered anodic aluminium oxide (AAO). The block copolymer separates the gold mesitylene as well as the developing gold nanoparticles from the AAO pore walls so that surface nucleation and pinning of gold clusters are prevented. Growing quasi-spherical gold nanoparticles locally deform the polymer chains irreversibly adsorbed on the AAO pore walls, and the polymer chains are pushed into the space between the gold nanoparticles. The gold nanoparticles have, therefore, larger diameters and smaller specific surface than hypothetical pluglike gold entities with the same volume, the formation of which is suppressed. Introduction Considerable efforts have been devoted to the generation and characterization of one-dimensional nanoparticle assemblies. 1 The formation of gold nanoparticle chains has turned out to be particularly challenging. Silica nanowires containing gold nanoparticle chains were obtained under the harsh conditions of vapour–liquid–solid (VLS) growth. 2–4 For example, silica, 5 gallium oxide, 6 and magnesium oxide 7 nanowires containing gold nanoparticle chains were reported to show strong wave- length-dependent and reversible photoresponse so that they may be used as wavelength-controlled optical nanoswitches. Draw- backs of VLS-based approaches are the necessity of high- temperature steps and the limited range of accessible matrix materials. One-dimensional assemblies of metal nanoparticles are also accessible under mild conditions by self-organization in the absence of shape-defining hard templates, either from pre- formed metal nanoparticles 8 or by one-pot syntheses starting from metal precursors. 9,10 However, spatial arrangement and alignment of the metal nanoparticle chains thus obtained are difficult to control. The generation of linear gold nanoparticle assemblies by conversion of gold precursors at moderate temperatures inside the cylindrical nanopores of shape-defining hard templates, 11 such as anodic aluminium oxide (AAO), has remained chal- lenging. If gold clusters are grown on amorphous alumina, nucleation takes place at defect sites, and the clusters are released once they have reached a critical size. 12 In non-epitaxial systems, even large Au clusters incommensurate with underlying substrates show extremely high mobility. 13 As a result, conver- sion of polar gold precursors, such as tetrachloroaurate, in AAO is accompanied by uncontrolled diffusion and coalescence of Au clusters, resulting in the formation of high-aspect-ratio gold plugs. 14 If solutions containing tetrachloroaurate and the block copolymer (BCP) polystyrene-block-poly(vinylpyridine) (PS-b- PVP), which are often used to generate two-dimensional arrays of gold nanostructures on smooth substrates, 15 are infiltrated into AAO, gold clusters will mainly develop at the hydroxyl- terminated AAO pore walls to which tetrachloroaurate and the polar PVP blocks segregate. 16 Here, we report a low-temperature bottom-up synthesis for locally ordered, linear assemblies of gold nanoparticles with narrow size distribution inside polymeric nanowires comprising thermolysis of the non-polar gold precursor gold mesitylene [Au 5 Mes 5 ]$2THF 17,18 and size-focusing particle ripening in the cylindrical nanopores of self-ordered AAO 19 in the presence of a Justus-Liebig-Universit € at Gießen, Institut f € ur Anorganische und Analytische Chemie, Heinrich-Buff-Ring 58, 35392 Gießen, Germany. E-mail: Sabine.Schlecht@anorg.chemie.uni-giessen.de b Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany c Institut f € ur Festk€ orperphysik, Technische Universit € at Berlin, Hardenbergstraße 36, 10623 Berlin, Germany d Institute of Physics, University of Halle-Wittenberg, Heinrich-Damerow- Str. 4, 06120 Halle, Germany e Fraunhofer Institute for Mechanics of Materials IWM, Walter-H€ ulse-Str. 1, 06120 Halle, Germany f Institut f € ur Chemie, Universit € at Osnabr € uck, Barbarastr. 7, D-46069 Osnabr € uck, Germany. E-mail: martin.steinhart@uni-osnabrueck.de; Fax: +49 541-9693324; Tel: +49 541-9692817 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c1jm14193g 684 | J. Mater. Chem., 2012, 22, 684–690 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. 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