A New Nanomechanical Cantilever Sensing Paradigm Using Piezoelectric Boron Nitride Nanotube-Based Actuation

Nanomechanical Cantilever Sensors (NMCS) have recently attracted a widespread attention for use in different nano- and micro-size applications such as studying the nanoscale surface topography by scanning probe microscopy and atomic force microscopy (AFM). In newer AFM systems, a sharp probe is placed at the tip of the microcantilever and a piezoelectric patch actuator deposited on the cantilever surface produces the movements of the probe above the examined surface. Similar system can be also utilized for mass sensing purposes by adding an unknown mass to the tip and measuring the beam deflection and the amount of shift in the resonance frequency that is caused by the addition of the tip mass. This sensing paradigm finds many applications in medical and biological fields such as DNA strand and bacteria weight measurement. However, one of the major issues in all piezoelectrically-actuated microcantilevers is the low actuation energy of the piezoelectric patch. Most of the current and widely used piezoelectric materials possess low mechanical characteristics such as low Young’s modulus of elasticity, low yield strength and most importantly incompatibility with most biological species and environment. It has been shown that both carbon and boron nitride nanotubes (CNT and BNNT) possess outstanding mechanical, chemical and electrical properties with acceptable piezoelectricity which make them suitable for microcantilever actuation applications. In this paper, a multi-physics multi-scale model is proposed in which the actuation of microcantilevers is produced by two sets of nanotube layers. Through extensive simulations, BNNTs were chosen to be used as the actuators because of their enhanced piezoelectric characteristics compared to CNTs. The modeling framework proposed here is used to investigate the effects of deposited tip mass with different weights on frequency response and resonance frequency of the microcantilever beam. These microbeams are made of aluminum or titanium materials and the results are compared with each other.