抄録
Nanometer-scale metal particles were directly coated with silica by a sol-gel method. The direct silica-coating did not require silane coupling agents that were often used in conventional silica-coating methods. For the silica-coated Au particles, the addition of tetraethylorthosilicate and water prior to ammonia was found to be critical to obtain a proper coating. The silica shell thickness was varied from 30 to 90 nm for TEOS concentrations of 0.0005 - 0.02 M at 10.9 M water and 0.4 M ammonia. For the silica-coated Ag particles, various amine catalysts were used for initialization of a sol-gel reaction of TEOS without need of a prior surface modification. Use of dimethylamine (DMA) as a catalyst was necessary to obtain a proper coating. The silica shell thickness was varied from 28 to 76 nm for TEOS concentrations of 1-15 mM at 11.1 M water and 0.8 M DMA. The optical spectra of the silica-coated Au and Ag nanoparticles agreed with predictions by Mie theory.
