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Highlights: [·] Impedance measurements on a microelectrode to detect transient cavitation. [·] Transient cavitation collapses determined to be of the order of 25Hz. [·] Diffusion layer thickness computed in the presence and absence of megasonic field. [ABSTRACT FROM AUTHOR]

Abstract: The application of megasonic energy in semiconductor cleaning solutions has been shown to be very effective in improving the particle removal efficiency (PRE). There has been a significant interest in understanding the phenomena of cavitation and acoustic streaming, which are known to play an important role in particle removal during megasonic cleaning. In the present work, transient cavitation in acoustically (∼1MHz frequency) irradiated aqueous solutions containing different dissolved gases (Ar, N2 and CO2) has been characterized with a 25μm diameter microelectrode using high resolution cyclic voltammetry. Specifically, using ferricyanide as an electrochemical probe, current transients are obtained as a function of time. A simple mathematical analysis based on diffusion is used to correlate the collapse characteristics of a transient cavity to the magnitude of current peaks and the time scale of rise and fall in current. [Copyright &y& Elsevier]

Abstract: High resolution chronoamperometry has been used to characterize the effect of two non-ionic surfactants, Triton® X-100 and NCW®-1002, on cavitation in aqueous solutions exposed to ∼1MHz sound field. Specifically, using ferricyanide as the electroactive species, temporal variation ofcurrent during itsreduction on a 25μm Pt microelectrode has been measured andis used to elucidate transient cavity behavior. The chronoamperograms for solutions exposed to megasonic field show current ‘peaks’ riding on the baseline current. These current ‘peaks’ have been attributed to the diffusion of ferricyanide species concentrated at the liquid–vapor interface of a transient cavity at the end of its collapse. In the presence of surfactants, the frequency of occurrence of current ‘peaks’ with magnitude ⩾0.3μA is found to increase indicating a higher number of transient cavity collapses. A simple mathematical model based on diffusion developed previously by the authors has been used to extract the maximum cavity size and range of distances between the center of the collapsing cavity and the electrode surface in the surfactant solutions. [Copyright &y& Elsevier]