Hydrogen as an optimum reducing agent for metallization of self-assembled monolayers

Abstract

We demonstrate a very efficient route for electroless deposition of Pd nanoparticles on self-assembled monolayers (SAMs) of a pyridine-terminated thiol. This method involves reduction of the coordinated Pd 2+ on SAMs by exposure to molecular hydrogen. A complete Pd adlayer surface coverage can be obtained. Moreover, this work is the first experimental demonstration of hydrogen adsorption on Pd adlayers.

Detection of Metal–Molecule–Metal Junction Formation by Surface Enhanced Raman Spectroscopy

“…39 Variations of the technique involve electrochemical reduction in low metal salt concentration 40 or the use of molecular hydrogen for a gentler reduction. 41 The concept was extended to more complicated structures such as a Pt-pyS-Pd-pyS-Au double-decker 42 and different linkers such as thiazole 43 or pyridine-terminated araliphatic thiols. 40,44 Here we use the Kolb method to prepare transition metal− pyS−gold junctions on SERS-active roughened gold and also investigate metal ions complexed to 4-mercaptopyridine adsorbed at gold nanoparticles.…”

Coordination controlled electrodeposition and patterning of layers of palladium/copper nanoparticles on top of a self-assembled monolayer

“…Patterning of Pd/Cu layer. It has been reported in previous STM studies of Pd deposition on top of pyridine terminated SAMs 25,31 that metal nanoparticles adhere very weakly to the SAM. The same also holds for the PdCu particles which combines favourably with the possibility to deposit them at high density as this offers the possibility of lithographic patterning and generating metallic nanostructures.…”

“…For this reason the second, much less explored deposition scheme is of interest as it relies on the chemical functionality of SAM molecules, thus promising a more active control of the deposition process. The key point is the electrochemical reduction of ions coordinated to a SAM which, similar to protocols where reduction is accomplished chemically, [22][23][24][25] follows a complexation step without potential control as illustrated in Figure 1b. The specific features of this coordination controlled electrodeposition (CCED) scheme are that (i) the amount deposited is defined by the SAM through the number of coordination sites, (ii) the metal clusters formed are localized on top of the SAM, and (iii) the potential provides a precisely adjustable parameter for controlling the deposition kinetics.…”

“…Originally performed in an electrolyte free of reactive species 26 (route A), this scheme has been modified and extended in various ways including the combination of electrochemical and electroless deposition. 24,25,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] In this context it is also worth noting that such a two step procedure of fixation of metal ion complexes and electroreduction in a non-reactive elec-trolyte has also been applied to generate metal nanoparticles on monolayer grafted carbon nanotubes or imbedded in layer by layer grown polymer films. [43][44][45] One variant of the complexation-reduction scheme, particularly important to the work presented below, is that the ions coordinated to the SAM can be reduced in the presence of metal ions in the bulk electrolyte ( Figure 1b, route B) using SAMs which exhibit the structural quality to suppress defect mediated deposition from the bulk electrolyte.…”

“…This not only simplifies the two step process of complexation and reduction of the coordinated ions to a one pot procedure but also makes multiple complexation-deposition cycles straightforward. 25,31 However, this approach offers the additional option of combining deposition from species coordinated to the SAM and present in the bulk electrolyte. This does not only overcome the limitation of a purely coordination mediated deposition with respect to the amount deposited but also provides unexplored ways for binary metal deposition if both a coordinating metal and a non-coordinating metal are present as illustrated by route B of Figure 1b.…”