For the first time, we studied the static and dynamic mechanical
response of CNT forests under electrostatic loading. Apparent
stiffening of the CNT forests after cyclic loading is attributed to
morphological change of straightening of the individual CNTs at the
top of the pillar in which the electric field penetrates, along with
relaxation of residual strains accumulated during the growth process.
Unlike common solid materials such as silicon that are used in
NEMS/MEMS devices, CNT forests are much softer and exhibit
significant energy dissipation due to internal damping by stick-slip
of CNT contact sites. The low stiffness and wide bandwidth of CNT
forests under resonance may suggest their use as soft resonant
elements that measure small forces over large contact areas, or that
electrostatically detect changes in surface conditions of CNTs such
as adsorption of molecular species. Thorough understanding of
those properties will enable new applications that leverage the
capability to design and fabricate CNT forest patterns using conventional
lithography and CVD methods.