Although site-selective deposition has been successfully demonstrated for a set of bimetallic systems, it is still impossible to detect and quantify the second metal being deposited on the surface of nanocrystal seeds while they are still suspended in the reaction medium. This work aims to turn the core-frame nanocrystals into a new platform for understanding the fundamentals involved in the heterogeneous nucleation and overgrowth of nanocrystals when the particles are still in the original growth solution. We hypothesize that the vibrational frequency of a metal-sensitive molecular probe can serve as a distinctive reporter for the metal being deposited on the edges of Ag nanocubes. To validate this hypothesis, we develop a novel class of probes based on isocyanide compounds (R-NC) for analyzing the heterogeneous nucleation and early-stage deposition of Pt atoms on the edges of Ag nanocubes by surface-enhanced Raman scattering (SERS). Because the SERS hot spots coincide with the sites for preferential heterogeneous nucleation at the edges of Ag nanocubes, the new paradigm allows for unprecedented sensitivity, with a lower detection limit below one monolayer. On the other hand, it is well known that the binding of the isocyanide group to a metal surface is similar to that of carbon monoxide, and thus the stretching frequency of the NC bond is dependent on the work function of the metal. We demonstrate that it is feasible to watch the heterogeneous nucleation and early-stage deposition of a metal on the edges of Ag nanocubes by following the stretching frequencies and intensities of the same isocyanide-based SERS probe. The success of this work will create new foundation for the design and rational synthesis of bi- and multi-metallic nanocrystals sought for a variety of applications.<br/>

Observing the overgrowth of a second metal on silver cubic seeds in solution by surface-enhanced Raman scattering

254th National Meeting (2017)

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