| AVS 56th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Monday Sessions |
| Session NS+BI-MoA |
| Session: | Nanowires and Nanoparticles II |
| Presenter: | C. Silien, University of Limerick, Ireland |
| Authors: | C. Silien, University of Limerick, Ireland M. Buck, University of St Andrews, UK S. Francis, University of St Andrews, UK M. Caffio, University of St Andrews, UK B. Wang, University of St Andrews, UK R. Schaub, University of St Andrews, UK D. Lahaye, University of Nottingham, UK N.R. Champness, University of Nottingham, UK |
| Correspondent: | Click to Email |
Metallization of organic self-assembled monolayers (SAMs) is generally impeded by the penetration of metal through the film. A two-step scheme, involving coordination of metal ions and electrochemical reduction in separate solutions [1], was recently proposed to circumvent the problem, opening up new opportunities for the preparation of low-dimensional metal structures on SAMs. This strategy was further investigated using SAMs of newly designed pyridine-terminated molecules (ω-(4-pyridine-4-yl-phenyl)-alkanethiol, PyPn, with n=2,3) [2], which combine the high structural integrity and quality of biphenyl-based SAMs [3,4] with the chemical functionality afforded by the pyridine moiety. Pd adlayers on PyPn SAMs on Au(111) were prepared by reduction of Pd2+ either directly from solution or following the two-step scheme [1]. Scanning tunneling microscopy (STM) revealed that, in both cases, and independently of the alkane spacer length, Pd systematically organizes into nanoparticles that are weakly bonded onto the pyridine moieties (i.e., easily displaced with tunnel current of the order of a few pA), exhibit a narrow height distribution around 2.4 nm and display a Coulomb gap of ~ ±0.20 V. These data strongly suggest that the Pd nanoparticles are not contacted with the Au substrate. Moreover, the nanoparticle coverage can be increased up to a monolayer, revealing that it is more favorable to generate new nanoparticles than to add material to existing ones. It is proposed that Pd2+ reduction is not mediated by structural defects in the SAM. Lateral diffusion of Pd adatoms and nanoparticles occurs on the SAM and explains the morphology of the Pd adlayer.
[1] Baunach, T.; Ivanova, V.; Kolb, D. M.; Boyen, H.-G.; Ziemann, H.-G.; Büttner, M.; Oelhafen, P. Adv. Mater. 2004, 16, 2024-2028.
[2] Silien, C.; Buck, M.; Goretzki, G.; Lahaye, D.; Champness, N. R.; Weidner, T.; Zharnikov, M. Langmuir 2009, 25, 959-967.
[3] Cyganik, P.; Buck, M.; Wilton-Ely, J. D. E. T.; Wöll, C. J. Phys. Chem. B 2005, 109, 10902–10908.
[4] Cyganik, P.; Buck, M.; Strunskus, T.; Shaporenko, A.; Witte, G.; Zharnikov, M.; Wöll, C. J. Phys. Chem. C 2007, 111, 16909–16919.