Nanomechanical cantilever active probes for ultrasmall mass detection

The objective of this study is to employ piezoelectrically driven nanomechanical cantilevers (so-called “active probes”) for ultrasmall mass detection. The idea originates from utilizing the unique configuration and the embedded piezoelectricity of active probes for high amplitude vibration, the attribute that is essential for precise measurement of ultrasmall mass by cantilever-based vibratory sensors. In this work, using focused ion beam technique, a small mass in the order of picograms is added at the tip of active probes. To detect the added mass, a precise model for modal characterization of the probe with geometrical discontinuities is utilized along with a parameter estimation technique for system identification. Using the shifts in the resonant frequencies of the identified system, the amount of added tip mass is estimated at the most sensitive mode of operation. Through a sensitivity analysis, it is shown that the second mode of the present configuration of the active probe is the most reliable mode for mass detection. Moreover, the effect of parameters’ uncertainties on the sensitivity of measurements is studied in more detail. Results indicate that system identification procedure proposed in this work is an inevitable step toward achieving precise measurement of ultrasmall masses through active probes with great potential in bio- and chemomass detection applications.