Fig. 5 shows the CDF values of both the types of silica
particles before and after ultrasonic cleaning, which were spread
on mica powder layers. The CDF values of both the types of
silica particles decreased after ultrasonic cleaning. This result
reveals that the surface-adhered nanoparticles increase the CDF
value. Since the amount of nanoparticle on nonporous silica is
considerably greater than that on porous silica, the decrease
ratio of the CDF value after ultrasonic cleaning depended on the
amount of surface-adhered nanoparticles