High frequency acoustic streaming is a promising technique for nano-scale particle removal from both flat and structured surfaces. Using DI water, the removal of nano-size particles down to 10 nm from flat surface was shown at a frequency above 1.3 MHz. As the frequency increases, the acoustic boundary layer thickness decreases and the streaming velocity increases thereby increasing the drag force and consequently the removal moment. By utilizing the electrical double layer force as a repulsive force (by using basic chemistry,) the removal of 10nm silica particles from flat surfaces can be accomplished using megasonic cleaning above 800 kHz. Oscillating flow induced vortex oscillation is essential to remove particles from structured surfaces. In the absence of particle deformation, 50nm PSL particle can be removed from a structured silica surface (a 1mm~* 1mm trench) using high intensity (25 W/cm~2) and high frequency (850 kHz) acoustic streaming.
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