Properties of Silicon and Metal Oxide Electrowetting Systems

Abstract

This paper is a review of our recent work on electrowetting properties of devices based on silicon (Si) and metal oxide (MO) electrodes. In particular, the electrowetting-on-dielectric (EWOD) properties of three- dimensional (3D) structured Si and MO electrodes are investigated and compared with those of planar ones. It is shown that the EWOD properties of these materials can be advantageously controlled by altering their geometry and/or their surface chemistry. Ultrafast laser irradiation was used in order to produce 3D superhydrophobic Si electrodes exhibiting double-scale roughness, in the micro- and nano-scales. The metal oxide electrodes were fabricated by depositing hydrophobic ZnO or TiO2 nanostructures onto the laser textured substrates using Pulsed Laser Deposition (PLD). The EWOD induced contact angle changes on the 3D structured surfaces show reversible or non-reversible behaviour depending on the geometry of the surface structures. Reversibility is observed when the double-scale roughness becomes more pronounced.

Keywords:

• Electrowetting
• Si
• ZnO
• TiO2
• PLD
• ultrafast lasers
• responsive surfaces
• hydrophobicity

Acknowledgements

Most of the work presented here was supported by the Integrated Initiative of European Laser Research Infrastructures LaserLab-II (Grant Agreement No. 228334). The authors thank Ms Aleka Manousaki for the FE-SEM images and Dr George Konstantinidis for the thermal evaporation of dielectric layers on metal oxides.