Figure 5.

Tuning the reaction rate of the Ag metal overgrowth and scaling up of the core–shell synthesis. (a) Structural formulas of the nonreactive, fully protonated (top) and reactive, deprotonated forms of ascorbic acid (bottom). The pK_a is 4.1. (b) Extinction spectra taken during Ag overgrowth on Au@SiO₂ NRs, which was performed in an acidified solution with 6 mM HCl. The spectra were recorded over 15 min with an interval between the spectra of 1 min. (c) LSPR peak intensity vs the reaction time when 2–8 mM HCl was present. (d) Plot of the reaction time versus the HCl concentration (mM). (e) Extinction spectra of the Au@Ag@SiO₂ NRs synthesized at a 1 mL (blue) and a 400 mL (red) scale.