The Modulation of Electrokinetic Streaming Potentials of Silicon-Based Surfaces through Plasma-Based Surface Processing

A new plasma processing-based methodology for enhancing the streaming potential (Vs) that may be obtained in electrokinetic flows for a given pressure gradient over a silicon surface-based microchannel is indicated. The dependence of the Vs on both the surface zeta potential and the electrolyte slip length was carefully determined through a series of experiments involving the variation of CF4- and Ar-based plasma parameters, incorporating pressure, exposure time, and power. It was determined through analytical estimates that, while the zeta potential is always increased, the slip length may be diminished under certain conditions. A record value of ∼0.1 mV/Pa was obtained using CF4 plasma at 500 W, 10 mTorr, and 300 s of exposure. The implications of the work extend to the investigation of whether smooth surfaces may be effective for generating large Vs’s for new modalities of electrical voltage sources in microfluidics-based applications.