Self-sensing Torsional Resonators Based on Inorganic Nanotubes

Nanoelectromechanical Systems (NEMS) couple electronics and mechanics at the nanoscale for a wide range of applications, as well as platforms for basic scientific research, offering unique opportunities to study properties of nanomaterials and observe quantum phenomena.

Inorganic nanotubes are natural candidates for key components in NEMS, due to exquisite mechanical and electronic properties. By twisting nanotubes, we distort the chirality and thus affect the electronic properties. Carbon nanotubes have been extensively studied in this context, but the study of the electromechanical behavior of inorganic nanotubes is still in its infancy. Here we present a study of the resonant electromechanical behavior of multi-wall tungsten disulfide (WS₂) nanotubes. Torsional resonators based on individual WS₂ nanotubes were fabricated, and the resonant torsional behavior of nanotubes was studied with optical and electrical characterization techniques.

We show for the first time that the resonance of WS₂ nanotube resonators can be detected in all-electrical means using an AC signal mixing technique. Detection is based on the piezoresistivity of the nanotubes, demonstrating that inorganic nanotubes can function as self-sensing NEMS. From the resonance spectra, we collect information on the mechanical behavior of WS₂ nanotubes in torsional resonance and deduce that they twist as solid rods, involving all or most of the layers in torsional vibration. The absence of interlayer friction suggests enhanced quality factors as compared to carbon nanotubes.

The results of this work demonstrate the potential of inorganic nanotubes for high frequency functional nanomechanical resonators. The findings pave the way for future basic research on the properties of inorganic nanotubes, as well as for their implementation in a wide range of nanosensors, such as accelerometers and gyroscopes.