By taking advantage of simple and low-temperature wet chemistry methods, researchers at the University of Roma “Tor Vergata” surprisingly found that the gentle contamination from the metallic package of commercial low-cost quartz crystal resonators can effectively promote the nucleation of ZnO nanowires on the silver electrodes without any seed layer. The nanowires are well separated, which is ideal for maximizing the active area and, thus, boosting the sensitivity of the device.
Using EDS, XRD, and PL measurements, the team verified that the weak contamination from the metallic package only results in low doping and that, despite the complex composition of typical metallic packages, iron species are likely responsible for the largely enhanced nucleation.
The fabrication process is extremely simple and low-cost, and, unlike previous approaches, does not pose risks for the integrity of high-frequency (that is, high-sensitivity) quartz resonators that are typically small, fragile and difficult to handle. Moreover, applying the single-step fabrication process to pre-packaged components results in ready-to-use high-performance sensors. As an example, the group applied this method to fragile quartz devices with resonant frequencies up to 20 MHz and obtained the highest ever-reported resonant frequency shift in response to immersion in both ethanol and water.
In conclusion, quartz sensors became ultra-sensitive by functionalizing their electrodes with ZnO nanowires, a process that was made easy by the gentle contamination from the package of low-cost commercial quartz resonators.