Gram-Scale Continuous Flow Synthesis of Silver-on-Silica Patchy Nanoparticles with Widely Tunable Resonances for Plasmonics Applications

Extensive researchhas been conducted on colloids thatincorporatenanostructured noble metals, motivated in particular by their highlytunable optical properties. However, the lack of approaches that offerreproducibility, tunability, and scalable production is limiting theirexploitation in many application areas. Here, we present an innovativeprocess for the controlled formation of silver patches on silica nanospheresusing gold nanocrystal seeds. The synthesis of the seeds and theirattachment in very small numbers to the silica spheres is achievedwithout employing any surfactants, stabilizers, or linker molecules.Using advanced transmission electron microscopy techniques, we showthat electroless deposition of nanostructured silver occurs at theintroduced seeds and leads to a central protrusion from the metalpatches not observed in earlier, seed-free work. We demonstrate thatboth seeding and growth processes can be achieved in millimixer flowreactors. With this simple and scalable approach, we provide compellingevidence for the use of seeds in producing targeted morphology andfunction. Specifically, patch size and optical properties can be tailoredin a predictive manner by adjusting the density of seeds on the silicananospheres as well as reagent concentrations during growth. As aresult, our process can be used to obtain colloidal dispersions withlocalized surface plasmon resonance peaks anywhere in the range 400to nearly 1300 nm. We confirm the scalability of our method by operatingthe growth process for around 70 min. Apart from changes in the firstfew minutes, the product properties remained rather stable and overa gram of high quality silver patch-coated silica could be recovered.Our approach opens up exciting new avenues for plasmonics applications,which typically require large amounts of nanoparticles with specificallydesigned optical properties. These include color and IR pigments,photocatalysts, and as light management components in optoelectronicdevices like photovoltaic cells.