The influence of molecular mobility on the properties of networks of gold nanoparticles and organic ligands.
We prepare and investigate two-dimensional (2D) single-layer arrays and multilayered networks of gold nanoparticles derivatized with conjugated hetero-aromatic molecules, i.e., S-(4-{[2,6-bipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)thiolate (herein S-BPP), as capping ligands. These structures are fabricated by a combination of self-assembly and microcontact printing techniques, and are characterized by electron microscopy, UV-visible spectroscopy and Raman spectroscopy. Selective binding of the S-BPP molecules to the gold nanoparticles through Au-S bonds is found, with no evidence for the formation of N-Au bonds between the pyridine or pyrazole groups of BPP and the gold surface. Subtle, but significant shifts with temperature of specific Raman S-BPP modes are also observed. We attribute these to dynamic changes in the orientation and/or increased mobility of the molecules on the gold nanoparticle facets. As for their conductance, the temperature-dependence for S-BPP networks differs significantly from standard alkanethiol-capped networks, especially above 220 K. Relating the latter two observations, we propose that dynamic changes in the molecular layers effectively lower the molecular tunnel barrier for BPP-based arrays at higher temperatures.
['Devid|Edwin J|EJ|', 'Martinho|Paulo N|PN|', 'Kamalakar|M Venkata|MV|', 'Prendergast|Úna|Ú|', 'Kübel|Christian|C|', 'Lemma|Tibebe|T|', 'Dayen|Jean-François|JF|', 'Keyes|Tia E|TE|', 'Doudin|Bernard|B|', 'Ruben|Mario|M|', 'van der Molen|Sense Jan|SJ|']
gold nanoparticles self-assembly aromatic capping ligands molecular charge transport surface enhanced Raman spectroscopy