Controlled removal of micro/nanoscale particles in submillimeter-diameter area on a substrate

In this paper, a removal method of micro/nanoscale particles in a submillimeter-diameter area at the interface between an aqueous suspension droplet and silicon substrate surface around a selectable point is proposed and demonstrated. It employs the acoustic streaming generated by an ultrasonically vibrating micro manipulating probe (MMP). The operating frequency of the device is 124.5 kHz, at which the micro manipulating probe oscillates approximately linearly. The experiments show that microscale particles with a diameter of 3-5 μm and nanoscale particles with a diameter of 300-500 nm in submillimeter-diameter areas can be removed in about 1.5 min. The principle of the cleaning method is analyzed by measuring the device's vibration mode and computing the 3D acoustic streaming field around the MMP. The diameter of cleaned area versus sonication time is clarified by experiments as well as the stable diameter of cleaned area versus vibration velocity. The dependency of the acoustic streaming field on the working parameters, which include the distance between the MMP's tip and substrate, the angle between the MMP and substrate, and the ratio of the normal vibration components of the MMP, is also investigated by the FEM (finite element method) computation. To the best of our knowledge, this is the first time to report a method for the removal of micro/nanoscale particles in a submillimeter range around a selectable point.