F. Sedona, M.M. Seyyed Fakhrabadi, M. Sambi
Università Degli Studi di Padova,
Keywords: diphenylacetylene, on-surface sunthesis, scanning tunelling microscopy, nanowires
Summary:Fabrication of nanomaterials is one of the pivotal challenges that researchers endeavor to find novel techniques for them. Due to the inherent and practical limitations of top-down techniques frequently applied to fabricate nanosystems, scientists try to reverse these prevalent techniques to bottom-up approaches to build the nanosystems from single molecules. Among a few limited number of bottom-up procedures, self-assembly has demonstrated tremendous potential opening new promising horizons in nanofabrication. Within this movement, one of the recent hot research topics is the formation of one- and two-dimensional on-surface structures via starting from rationally selected single hydrocarbon molecules and extending to nanowires and nanomeshes of carbon allotropes by exploitation of benefits of self-assembly and surface-assisted covalent bonding thereafter [1-3]. As a result of the importance of carbon-based nanomaterials, researchers all over the world have been working on synthesis and characterization of one, two and three dimensional micro/nanostructures made of carbon atoms and their allotropes [4-8]. In this study, on-surface synthesis of large scale ordered diphenylacetylene based nanowires on Ag(110) is reported. Fig. 1 illustrates the 1D on-surface polymerization steps starting from 1,2-bis(4-bromophenyl) ethyne (DBPE) molecules, schematically. As shown in this figure, the DBPE molecules deposited on Ag(110) substrate create organo-metallic nanowires. The bromine atoms detach from the molecules as soon as they touch the Ag(110) surface due to the catalytic activity of the substrate and the silver atoms replaces them. Annealing the deposited surface at higher temperatures results in release of the silver atoms and synthesis of organic nanowires. Fig. 2 (a) and (b) shows the ultra-high vacuum STM images of as-deposited and annealed phases of the molecules and nanowires and their corresponding models.. As shown in Fig. 2 (a), the silver atoms (blue spots) replaced the bromine atoms (red spots) on two ends of the DBPE and created the organo-metallic nanowires. The dissociated bromine atoms occupied two positions: (a) between two adjacent silver adatoms and (b) in free space between the triple bonds. Fig. 2 (b) shows that after annealing the organo-metallic nanowires release the silver adatoms resulting in production of continuous organic nanowires characterized by the alternation of two benzenes and one triple bond. References  P. Ruffieux et al., Nature, 2016, 531(7595), 489.  L. Talirz et al., Adv. Mater., 2016, 28, 6222.  J. Cai et al., Nature, 2010, 466 (7305), 470.  H. Zhang et al., J. Ame. Chem. Soc., 2015, 137 (12), 4022.  J. Cai et al., Nat. Nanotech., 2014, 9 (11), 896.  A. Basagni et al. J. Am. Chem. Soc., 2015, 137, 1802.  A. Basagni et al., Chem.–A Euro. J., 2014, 20 (44), 14296.  Colazzo et al., J. Ame. Chem. Soc., 2016, 138 (32), 10151.