Photoelectrowetting

This has electrical and optical properties similar to the metal/insulator/semiconductor stack used in metal–oxide–semiconductor field effect transistors (MOSFETs) and charge-coupled devices (CCDs).

At zero bias (0V) the conducting droplet has a large contact angle (left image) if the insulator is hydrophobic.

In the presence of light (having an energy superior to the band gap of the semiconductor) the droplet spreads out more due to the reduction of the thickness of the space charge region at the insulator/semiconductor interface (right image).

Photoactuation of microelectromechanical systems (MEMS) has been demonstrated using photoelectrowetting.,[4][5] A microcantilever is placed on top of the liquid-insulator-photoconductor junction.

This wireless actuation can be used as a substitute for complex circuit-based systems currently used for optical addressing and control of autonomous wireless sensors[6] Photoelectrowetting can be used to circulate aqueous solution-based sessile droplets on a silicon wafer covered with silicon dioxide and Teflon – the latter providing a hydrophobic surface.