Tip-Induced Local Metal Deposition

A remarkable feature of the clusters generated by the present procedure was their unusual stability. In fact, it was found that Cu nanoclusters generated on Au(lll) surfaces presented the amazing property of remaining stable at potentials above the reversible dissolution potential for bulk Cu (Kolb et ah, 2002). 

This is not easy to understand, since on thermodynamic grounds clusters should be less stable than the bulk material. It is possible that clusters generated by electrochemical nanostructuring may undergo a certain degree of alloying with the material of the surface that could increase their stability. Indeed, Monte Carlo simulations show that if achievable, such alloying will improve the stability of the clusters toward dissolution. 

An alternative type of tip-induced nanostructuring has recently been proposed. In this method, a single-crystal surface covered by an underpotential-deposited mono-layer is scanned at a close tip-substrate distance in a certain surface area. This appears to lead to the incorporation of UPD atoms into the substrate lattice, yielding a localized alloy. This procedure works for Cu clusters on Pt(l 11), Pt(lOO), Au(l 11), and for some other systems, but a model for this type of nanostructuring has not been available until now. (Xiao et al., 2003). 

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FIGURE 36.1 Schematic illustration of some electrochemical techniques employed for surface nanostructuring (a) tip-induced local metal deposition (b) defect nanostructuring (c) localized electrochemical nucleation and growth d) electronic contact nanostructuring. 

A so-called tip-induced local metal deposition" was recently achieved in systems k i hkt)/C and Ag(/i /)/Cu with hkt) - (100), (111) using the in situ STM technique by Kolb et al. [6.187, 6.188]. First, a certain amount of metallic copper is cathodically deposited on the tip. Copper is then transferred fi-om the tip to the substrate by bringing the tip closer to the substrate surface. Originally, this was achieved by pulse polarization changing the sign of the tunneling voltage, f/r. The... 

In addition to analytical applications for monitoring surftice structures and dynamics STM can also be used as a tool for the deliberate modification of electrode surfaces on the mesoscopic scale. By applying appropriate signals to an STM tip, local metal-deposition reactions can be induced from metal-ion-containing solutions [12, 15, 16]. As an example. Fig. 8 shows a platinum particle on an HOPG surface, which was... 

Fig. 37. Localized tip-induced in-situ metal deposition (a) Ensemble of Ag pillars deposited on graphite (after [177]). (b) TVain of Cu dots deposited on Au (after [179]). (c) Au dots grown on p-GaAs at positive tip and with light. Size is SOOAxSOOA (after [150]).

The powerful combination of SECM with ITIES electrochemistry has enabled the spatially controlled deposition of metal particles, which is potentially extendable to nanoparticle (NP) deposition by using a nanotip. Eor instance, Ag particles were locally electrodeposited on a conductive substrate by employing a micropipet-supported ITIES tip in the egress IT mode (Eig. 9c). The spatial resolution of the tip-induced electrodeposition is controlled by the tip size and the tip-substrate distance. A shorter distance can be maintained by monitoring a shear force between the micropipet tip and the substrate to improve the spatial resolution. An even higher spatial resolution can be achievable by the shear-force-based control of a submicrometer-sized ITIES tip. ... 

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