Wettability Modulation of Graphene Nanodrums by Current Bias

In this work, an array of nanopores (diameter: 1000 nm, depth: 200 nm) is fabricated in silicon oxide (SiO2) substrate. The contact angle (CA, ~ 83.3o) of water droplet (1 μL) on the SiO2 nanopore array is found larger than that (~ 61.5o) on normal SiO2, indicating that the SiO2 nanopore array has changed the surface wettability of SiO2. Then a few-layer graphene membrane is synthesized by chemical vapor deposition (CVD) and transferred onto the SiO2 nanopore array, many graphene nanodrums (GNs) are formed. The CA of water droplet on GNs is measured to be 94.0o, which shows that the surface wettability of SiO2 nanopore array has been changed from hydrophilic to hydrophobic state by the graphene membrane. When a current is applied to flow through the graphene membrane, the CA of water droplet on GNs becomes smaller than 90o, which is a hydrophobic-to-hydrophilic transition. It is also found that the CA of water droplet on GNs decreases as the current increases. These above observations show that the wettability of GNs can be modulated by current bias. The mechanism for these experiment phenomena is discussed, which is attributed to the role of water electrolysis.