Figure 6.

In situ etching of core–shell metal(oxide)–silica nanoparticles by exposure to a 100 mM NaOH aqueous solution with a flow rate of 5 μL.min^–1. (A) Au–silica. (B) Wet etching of Fe₃O₄ core/WORM silica core/shell nanospheres into yolk–shell particles under the flow of a basic aqueous solution. At the left, particles at the start of the experiment. At the center, yolk–shell particles formed after 165 and 330 min of exposure to the basic solution by the etching of the silica shell. Different areas were imaged in both (A) and (B) due to beam sensitivity (total accumulated dose of 1.5 × 10³ e^–nm^–2). At the right, experimental observation of the “free” diffusion of the catalytic cores. The white arrows highlight single cores rattling though the void of the yolk–shell particle.