Two types of commercially available silica—porous silica
(CCIC, purity: 99.4%, mean diameter: 5 μm, silica microbeads
P-1500) and nonporous fused silica (Denki Kagaku Kogyo Co.,
Ltd., purity: 99.5%, mean diameter: 4.5 μm, FB-6S)—were
used in this study. Fig. 1 shows the field emission scanning
electron microscopy (FE-SEM) observations of the surfaceadhered
nanoparticles before and after performing ultrasonic
cleaning: before the cleaning of (a)