Principle Scientist: Dr. Robert Dryfe, University of Manchester, Department of Chemistry.
R.A.W. Dryfe*, E.C. Walter, and R.M. Penner*, Electroless Deposition of Metal Nanostructures Powered by Insoluble Crystals of a Ferrocene Derivative, ChemPhysChem 12 (2004) 1879.[PDF]
We've discovered that metal nanostructures, inclouding nanowires, can be prepared by galvannic displacement, which involves the concurrent oxidation of an insoluble organic crystal and the reduction of metal ions at a stepped graphite surface. Two aspects of the reported results are novel: First, the Galvanic displacement of nanostructures was powered by the concurrent oxidation of insoluble layers of ferrocene derivatives. The organic material was pre-deposited onto the graphite surface prior to immersion in the aqueous metal plating bath. Second, the method described here ÒautomaticallyÓ produced metal nanostructures without external intervention to control the growth potential or growth time. The experiment described here constitutes an extension of the seminal prior work of Bond, Scholz, and others. who have explored the solid-state electrochemistry of insoluble crystalline overlayers in great detail.
Scheme 1.Proposed mechanism by which metal is electrodeposited from a perchlorate-containing electrolyte onto an HOPG surface on which decamethyl ferroene crystals reside.
Specifically, we found that overlayers of two ferrocene derivatives, when deposited on HOPG surfaces, are capable of driving the electrochemical deposition of metal nanoparticles and nanowires. The mechanism responsible for this metal deposition is shown in Scheme 1, is a Galvanic displacement driven by the coupled oxidation of these organic crystals. Attention is focused in this paper on the nature of the metal deposit and on the mechanism of the deposition reaction. Scanning electron microscopy (SEM) was used to monitor the distribution both of organic crystallites and the deposited metal on the graphite surface. Electrochemical measurements coupled with energy dispersive x-ray analysis (EDX) were used to verify the mechanism of the deposition process.
Figure 1.Energy dispersive X-ray fluoresence analysis (EDX) of a graphite surface on which decamethyl ferrocene crystals had been deposited. The spectrum of (a) was acquired after exposure to aqueous (NH3)2Cl4Pd in aqueous 0.10 M KI, (b) aqueous (NH3)2Cl4Pd in 0.10 M LiClO4, (c) aqueous 0.10 M KI, and, (d) aqueous 0.10 M LiClO4.
How do we know that the reducing equivalents required for metal deposition are derived from the decamethyl ferrocene? Control experiments rule out electroless palladium deposition. But direct evidence is provied by EDX elemental analysis of the surface, shown in Figure 1. These data permit us to directly observe the incorporation of the anion into the decamethyl ferrocene, and the observation of this anion (chloride or iodide in Fig. 1) in emersed surfaces.One application for this idea may be for the anodic-protection of oxidation-prone nanostructures located in circuits.
