Bidirectional migration of Au colloids and silicon microrods in liquid using asymmetrical alternating current electric field with insulated electrodes

Abstract

In this study, we demonstrate the migration of Au colloids and silicon microrods in deionized (DI) water and isopropyl alcohol (IPA) by applying asymmetrical AC bias to two electrodes capped with a thin dielectric film. Both Au colloids and silicon microrods successfully migrate from one electrode to the other when asymmetrical AC bias is applied to the electrodes. Furthermore, the direction of the migration can be easily reversed by inverting the wave form. The insulated electrodes have the potential to prevent contamination and bubbling originating from electrochemical reactions, which makes the adoption of the technique for mass production processes easy and realistic. The bidirectional migration acts similarly to electrophoresis and is effective even in DI water and IPA in which conventional DC electrophoresis with insulated electrodes is ineffective. This technique is widely applicable to the positional control of small objects including nano- and micro-sized devices.

Orientation- and position-controlled alignment of asymmetric silicon microrod on a substrate with asymmetric electrodes

“…If the charge amount of the electric double layers follows the AC bias, the electric field from the electrodes is screened and weakened, which results in a decrease of the attractive forces, F ES1 and F ES2 , and increase of the gap between the Si microrod and the electrodes. For DI water, the time constant of the induced charge in the electric double layer is 5 ms, 29) which means that the equivalent circuit shown in Fig. 5(a) is valid for DI water at 50 kHz.…”

“…17) If the electrodes are insulated, however, the DC bias is immediately screened by an electric double layer. 29) Therefore, the electrodes have to be bare to maintain the DC electric field in a fluid and the torque for the orientation control.…”