Mode coupling, bi-stability, and spectral broadening in buckled nanotube resonators
Bi-stable mechanical resonators play a significant role in various applications, such as sensors, memory elements, and quantum computing. While carbon nanotube (CNT) based resonators have been widely investigated as promising nano electro-mechanical devices, a bi-stable CNT resonator has never been demonstrated. Here, we report a new class of CNT resonators in which the nanotube is buckled upward. We show that a small upward buckling yields record electrical frequency tunability, whereas larger buckling can achieve Euler-Bernoulli (EB) bi-stability, the smallest mechanical resonator with two stable configurations to date. We believe that these recently discovered CNT devices will open new avenues for realizing nano-sensors, mechanical memory elements and parametric amplifiers. Furthermore, we present a three-dimensional theoretical analysis revealing significant nonlinear coupling between the in-plane and out-of-plane static and dynamic modes of motion, and a unique three-dimensional EB snap-through transition. We utilize this coupling to provide a conclusive explanation for the low quality factor in CNT resonators at room temperature, key in understanding dissipation mechanisms at the nano scale.