  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.
