Guiding Principles in the Galvanic Replacement Reaction of an Underpotentially Deposited Metal Layer for Site-Selective Deposition and Shape and Size Control of Satellite Nanocrystals

The combination of sustained under-potential deposition (UPD), galvanic replacement reaction, and control of nanocrystalline growth, is a versatile strategy for engineering the architectural diversity of complex heterogeneous metallic nanocrystals (HMNCs). The strategy has the potential to generate a large variety of HMNC structures if the causality between reaction parameters and architectural elements can be identified and sufficiently understood. We have discovered three guiding principles which are useful for the control of site-selective deposition and the shape and size of the satellite nanocrystals (NCs). These principles are illustrated here in this article using Au/AgPd HMNCs consisting of a Au central NC and AgPd satellite NCs as examples. The three principles are (1) full corner- or edge-selective deposition requires an adequate supply of Ag + in the reaction solution to sustain the presence of a Ag UPD-layer, the galvanic oxidation of which supplies electrons to the corners or edges of a central NC for a full-island growth; (2) in full corner- or edge-selective deposition, the shape of the satellite NCs can be controlled by the dependence of the growth kinetics of Pd and Ag atoms on exposed facets, {100} facets for Pd and {111} facets for Ag; and (3) the size of the satellite NCs can be controlled by varying the total precursor (Ag + Pd) concentration at a fixed Ag/Pd concentration ratio so long as the requirements for site-selective deposition and shape control are satisfied. The findings presented here could rationalize the design and synthesis of architecturally distinct HMNCs based on the newly developed UPD-layer-induced galvanic replacement reaction.