Aug 13, 2013
ZnO nanowires and low-cost quartz resonators: a perfect match
Researchers have long tried to integrate arrays of well-separated nanostructures on the electrodes of quartz resonators, as the sensitivities of micro-balances ultimately depend on the effective electrode area. Reporting their results in the journal Nanotechnology, scientists in Italy have come up with a promising approach that makes use of affordable apparatus and avoids complicated processing steps.
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.
Full details can be found in the journal Nanotechnology 24 355503
About the author
The study was conducted at the University of Tor Vergata, Rome, Italy, and was financially supported by the Italian Institute of Technology (Project Seed "API NANE") and by the Italian Ministry for University and Research (FIRB – Futuro in Ricerca 2010). All of the authors contributed to the design of the experiments and the writing of the paper. Dr Andrea Orsini, lead author, synthesized the nanowires and characterized them by SEM, EDS, and network analyzer. Prof. Pier Gianni Medaglia, David Scarpellini, and Prof. Roberto Pizzoferrato performed XRD and PL experiments. Prof. Christian Falconi (corresponding author, email@example.com) is the leader of the PiezoNanoDevices team at the University of Tor Vergata.