Tip size effect on the appearance of a STM image for complex surfaces: Theory versus experiment for Si(111)-(7x7)

The frequency dependence of the electrorheological response was studied experimentally in a suspension of barium titanate spherical particles suspending in silicone oil. In the system, only one factor, namely the frequency of the applied electric field, affects the electrorheological effect. The experimental data reflect the frequency effect more reliably and more accurately. Under the sinusoidal electric fields, the shear stress increases sharply with frequency below 500 Hz and reaches a saturated value beyond 500 Hz. The phenomena can be explained well with the permittivity mismatch theory. More experiments indicate that the electrorheological effect should be the sum of the mismatch polarization and the interfacial polarization.