Preparation of Photoluminescent Porous Silicon Nanoparticles by High-Pressure Microfluidization

The use of high-shear microfluidization as a rapid, reproducible, and high-yield method to prepare nanoparticles of porous silicon (pSi) with a narrow size distribution is described. Porous films prepared by electrochemical etch of a single-crystal silicon wafer are removed from the substrate, fragmented, dispersed in an aqueous solution, and then processed with a microfluidizer, which generates high yields (57%) of pSi nanoparticles of narrow size distribution (PDI = 0.263) without a filtration step. Preparation of pSi nanoparticles via microfluidization improves yields (by 2.4-fold) and particle size uniformity (by 1.8-fold), and it lowers the total processing time (by 36-fold) over standard ultrasonication or ball milling methods. The average diameter of the nanoparticles can be adjusted over the range 150-350 nm by appropriate adjustment of processing steps. If the fluid carrier in the microfluidizer contains an oxidant for Si, the resulting pSi particles are prepared with a core-shell structure, in which an elemental Si core is encased in a silicon oxide shell. When an aqueous sodium tetraborate processing solution is used, microfluidization generates photoluminescent core-shell pSi particles with a quantum yield of 19% in a single step in less than 20 min.