Selective plasma-induced deposition of fluorocarbon films on metal surfaces for actuation in microfluidics

The present work focuses on the selective deposition of fluorocarbon (FC) films on metal surfaces, aluminum in specific, over SiO2 surfaces, in order to obtain surfaces of distinct wettability. If this is achieved, hydrophobic/hydrophilic patterning of substrates would be feasible by means of a self-aligned and relatively simple method. For the selection of conditions appropriate for selective deposition of FC films on Al over SiO2, plasma parameters such as plasma power, bias voltage, electrode temperature, and gas composition were varied. The selectivity of the deposition is optimized through proper selection of the deposition conditions, mainly gas mixture composition and deposition time, and is demonstrated by means of contact angle measurements on Al and SiO2 surfaces. Contact angles are measured without and with voltage application between the droplet and the surface to induce electrowetting. Contact angles vary as a function of the applied voltage and in combination with measured contact angle hysteresis dictate the voltage range necessary for droplet actuation. The results demonstrate that optimization of the electrowetting properties of such plasma-deposited films is necessary for rendering feasible the use of such films in electrowetting-based actuation of microfluidic devices with application of relatively small voltages