Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles

Abstract

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.

Interplay Between Mechanochemistry and Sonochemistry

“…Bubbles vibrating at 20 kHz as source of microstreaming are capable of breaking erythrocites which leak haemoglobin when shear stress exceeds 450 Pa [109] (Figure 20). Similar conclusions on the negligible effect microstreaming has on biofilm disruption have been reached by Fernandez Rivas et al using a small-scale ultrasonic device with the ability of locally remove layers of metals, polymers or biomaterials from a glass slide (Figure 21) [110,111]. The innovative idea here is the use of a silicon surface containing micropits where individual gas bubbles can be entrapped.…”

“…2.5 times larger than in other crystallographic orientations after 180 min of irradiation. Erosion pits increased at a constant rate for (110) and (111), although this effect stopped in (100) after 120 min.…”

“…Material removal experiments have been conducted using the setup shown in Figure 21 (top) for the elimination of biofilms [110]. The cavitation cell does not enable an optical visualization of the cavitating bubbles due to the opaque character of materials deposited on the glass slide.…”

“…On the other hand, Cr and Ti did not undergo reaction after 10 min of irradiation. The latter allows to conjecture that any contribution from radical species (such as H· or HO·) to the removal rates will be minimal under the conditions employed to produce cavitating bubbles, which nucleate from the pits [110].…”

“…Silicon is an oft-studied case where surface erosion has been studied in various crystallographic orientations; namely (100), (110) and (111) surfaces at 191 kHz [136]. The most significant damage caused by cavitation was observed on the (100) face, with an eroded area which was ca.…”