Improved production efficiency of mesoporous silicon nanoparticles by pulsed electrochemical etching

• A miniature ball milling system with a maximum of ten samples was introduced.
• Pulsed electrochemical etching produces fragile layers in porous silicon films.
• Milling parameters were optimized to produce porous silicon nanoparticles.
• The fragile layers improved the yield of the nanoparticles of a specified size.

The nanoparticles produced by top down methods possess typically considerably wide size distributions. However, monodispersive nanoparticle suspensions are essential for many applications. This is also true for mesoporous silicon nanoparticles, which can be produced by grinding the electrochemically anodized porous films in planetary ball mills. Herein, we report a method to control the particle size of porous silicon nanoparticles already prior to the milling. The method is based on fragile layers that are produced in the porous silicon film by repetitive pulsed electrochemical etching during porosification of silicon. The thin fragile layers separating the layers with normal porosity in the porous films guide the breakage of the films preferentially into the particle size corresponding to the distance of the adjacent fragile layers. The production method was evaluated in terms of the yield and particle size distributions. The distance of 173 nm between the fragile layers increased substantially the yield of the corresponding nanoparticle sizes (122 nm) with the short milling time of 2 min. The milling was performed with an insert located in the normal milling jar so that glass vials could be used with smaller sample sizes. The present study paves the way for more effective production of mesoporous silicon nanoparticles which is applicable also for other corresponding nanomaterials.

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