Strain relaxation and resonance of carbon nanotube forests under electrostatic loading

Abstract

Electrostatic loading is widely used for sensing and actuation in miniaturized electromechanical systems, yet classical designs involve geometric patterning of solid materials such as silicon and metal films. Conductive nanoporous materials for electrostatics may enable engineering of new functionalities arising from their compliance, internal surface forces, and high surface area. Toward this end, we investigate the response of vertically aligned carbon nanotube (CNT) "forests" to DC and AC electrostatic loads. First,

Self-Sensing WS2 Nanotube Torsional Resonators

“…This observation implies that both resonance modes are associated with dominant rotational motion. Notably, the simulation also reveals small resonance peaks at half resonance frequencies, which is typical for electrostatic force excitation, since the force is proportional to V 2 (see the relevant discussion in our previous publication). Briefly, the application of an electrostatic field induces force having two frequencies: the excitation frequency (which is proportional to V bias V ac ) and twice the excitation frequency (which is proportional to V ac 2 ).…”

“…The electrostatic force and moment applied to the paddle were extracted from the capacitance, by calculating the derivatives of the electrostatic co-energy U = CV 2 /2, where C is the capacitance and V is the excitation voltage, with respect to the linear deflection and the rotational motions (similar calculations were demonstrated elsewhere , ), such that The equations of motion derived from variational principles are where I and m are the mass moment of inertia and the mass of the paddle, respectively, e is the offset of the nanotube from the paddle center of mass (Figure c), and c θ and c u are the coefficients of damping associated with motion in the θ and u directions, respectively. Importantly, the equations of motion demonstrate the coupling between the two degrees of freedom due to the offset e , which implies that under dynamic excitation of the device both θ and u appear.…”

“…Notably, the self-sensing resonance frequency showed excellent agreement with the electrostatic measurements, where the half-resonance frequency of the first resonance mode was obtained at 5.3 MHz. Importantly, although the excitation frequency is half the resonance frequency, the device vibrates in its resonance frequency; thus, Figure c presents a resonance response, as was observed in many electrostatically excited devices …”

Heat transfer of graphene foams and carbon nanotube forests under forced convection

“…As explained above, high velocities increase the dimensions of the boundary layers, which, in turn, limits the heat transfer in the horizontal direction and enhances heat transfer in the vertical direction. Organized CNT forests have fewer CNT-CNT interaction sites (as indicated elsewhere [35]), which have been reported to induce scattering of hot phonons and reduction of the heat transfer [17,36], [37]. Thus, higher velocities further enhance the vertical heat transfer in organized CNT forests.…”

Multiscale Elasticity of 3D Boron Carbonitride Foam for Tunable Mechanical Resisting Devices

“…For example, while monolayer graphene has a very high Young’s modulus (∼1 TPa), Young’s modulus of GF was found to be dramatically lower in the order of a few kilopascals . Similarly, while an individual carbon nanotube exhibited Young’s modulus that can reach values similar to those of graphene, the elastic behavior of the carbon nanotube forest was found to be dominated by the interactions between the individual tubes (i.e., interactions between graphene layers), and accordingly, it presented Young’s modulus of ∼1 MPa . The interactions between graphene and BN layers were demonstrated elsewhere, where the torsional stiffness (i.e., the resistance of the material to rotational interlayer shearing) of BN nanotubes was found to be at least an order of magnitude higher than that of carbon nanotubes (composed of folded graphene layers), showing that the interlayer interactions of BN are significantly higher than those of graphene …”