Magnetite nanoparticles with an 8-nm average size infiltrated into the pores of porous silicon. The distance between the particles is near 4 nm (twice the thickness of the coating). The concentration of the particle solution was 8 mg Fe/ml. The image shows a cross-sectional region near the pore tips.
Rumpf et al. Nanoscale Research Letters 2012 7:445 doi:10.1186/1556-276X-7-445