ZnO Nanowires for Feedback-Assisted Tuning of Electromechanical Resonators.

The fabrication of devices with accurately controlled properties almost invariably takes advantage of feedback so that, based on real-time measurements, process parameters can be automatically adjusted in order to obtain the desired characteristics. Nevertheless, despite the outstanding advantages of wet-chemistry methods (e.g., simplicity, low-cost, low-temperature, and compatibility with almost any process and type of substrate), the use of feedback in the solution growth of nanostructures is almost unexplored. In fact, conventional techniques for the real-time in-liquid characterization of nanostructures are extremely complex and can introduce intricate artefacts. Here, by taking advantage of an electro-mechanical resonator as a substrate, we on-line monitor, at the system level, the nanostructure growth, thus enabling the feedback-assisted tuning of low-cost electro-mechanical resonators by ZnO nanowires. This approach allows for post-fabrication tuning of the resonant frequency with high accuracy and high tuning range (e.g., about 1% in our experiments) in a simple, fast, low power, and low-cost manner, without requiring expensive facilities such as clean rooms or high-vacuum deposition systems. Moreover, remarkably, we find that for a given desired resonant frequency, the quality factor of the resonance can be separately adjusted by modifying the nutrient solution, which can be a key advantage for filters. The straightforward interfacing and packaging of the final resonator stems from the large difference, about 5 orders of magnitude, between the key structure dimensions, namely, the diameter of the ZnO nanowires and the much larger (e.g., few millimeters) diameter of the quartz. Our results can lead to the widespread application of nanowire-tuned electro-mechanical oscillators and filters in electronics, sensors, and material science.