Figure 5.

In situ etching of silica model nanoparticles by exposure to a 100 mM NaOH aqueous solution with a flow rate of 5 μL·min^–1. (A) Stöber silica. Particles became hollow when exposed to a flow of 100 mM NaOH. right: The intensity profile along the nanoparticle shown in the inset. No expansion was observed (a total accumulated dose of 1.4 × 10⁴ e^–nm^–2). Inset scale bar: 50 nm. (B) WORM silica nanospheres under a flow of 100 mM NaOH. Due to the small size of the particles (40 nm), our results indicate that the silica network was strongly affected even in a single frame (a total accumulated dose of 1.5 × 10³ e^–nm^–2). Therefore, different areas needed to be imaged to study how WORM silica nanospheres etched under basic conditions. Particles showed hollowing after 390 min of exposure to the basic solution. right: Intensity profiles of two selected nanoparticles showing the formation of a hollow volume inside the particle, with minimal change in total size of the nanoparticle. Similarly as reported before for these particles systems.¹⁶