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A unique feature of two-dimensional (2D) materials is the ultralow friction at their van der Waals interfaces. A key question in a new generation of 2D heterostructure-based nanoelectromechanical systems (NEMS) is how the low friction interfaces will affect the dynamic performance. Here, we apply the exquisite sensitivity of graphene nanoelectromechanical drumhead resonators to compare the dissipation from monolayer, Bernal-stacked bilayer, and twisted bilayer graphene membranes. We find a significant difference in the average quality factors of three resonator types: 53 for monolayer, 40 for twisted and 31 for Bernal-stacked membranes. We model this difference as a combination of change in stiffness and additional dissipation from interlayer friction during motion. We find even the lowest frictions measured on sliding 2D interfaces are sufficient to alter dissipation in 2D NEMS. This model provides a generalized approach to quantify dissipation in NEMS based on 2D heterostructures which incorporate interlayer slip and friction.

Waveguides for mechanical signal transmission in the megahertz to gigahertz regimes enable on-chip phononic circuitry, which brings new capabilities complementing photonics and electronics. Lattices of coupled nano-electromechanical drumhead resonators are suitable for these waveguides due to their high Q-factor and precisely engineered band structure. Here, we show that thermally induced elastic buckling of such resonators causes a phase transition in the waveguide leading to reversible control of signal transmission. Specifically, when cooled, the lowest-frequency transmission band associated with the primary acoustic mode vanishes. Experiments show the merging of the lower and upper band gaps, such that signals remain localized at the excitation boundary. Numerical simulations show that the temperature-induced destruction of the pass band is a result of inhomogeneous elastic buckling, which disturbs the waveguide's periodicity and suppresses the wave propagation. Mechanical phase transitions in waveguides open opportunities for drastic phononic band reconfiguration in on-chip circuitry and computing.

This talk presents the benefit of buckling in strongly tuning nonlinear MEMS resonators. In particular, the talk shows experimental buckling achieving more than 230% tuning in the natural frequency of drumhead MEMS resonators. Moreover, the experiments demonstrate that buckling switches the frequency response between purely stiffening, purely softening, and stiffening-to-softening nonlinearities. We tune the buckling state in these experiments by controlling the electric voltage and the temperature of the resonators. Therefore, these resonators undergo electrostatically-mediated thermoelastic buckling where specific combinations of temperature and voltage are required to access the distinct vibrational responses. We explain the observed linear and nonlinear responses by a reduced-order model (ROM) that lumps the resonator into a 1-degree-of-freedom mass connected to springs reflecting bending, stretching, electrostatic forces, thermal expansions, and residual stresses. The ROM mimics von Mises trusses to model the buckling in the membrane resonators without the need for exact geometry or structure to model the resonators. This developed ROM and the electro-thermoelastic buckling tunability present useful applications for on-chip acoustic devices in different fields such as signal manipulation, filtering, and MEMS waveguides.

Two-dimensional (2D) van der Waals materials are both highly deformable atomic membranes and electrically active quantum materials. Most electronic and quantum states in both monolayer 2D materials and heterostructures are highly sensitive to strain and interlayer structure, and thus may be tuned mechanically. Here we explore the current frontiers using 2D material mechanics to sense, tune, tailor or even reconfigure electronic properties, device behavior and quantum states. We compare the relative impacts of different kinds of mechanical perturbations including in-plane strain, out-of-plane vibrations, inhomogeneous three-dimensional deformations, instabilities of membranes under compression like crumpling and wrinkling, and interlayer slip. Throughout, we explore how each form of coupling may be used for applications that cannot be realized in the flat unperturbed materials including tunable nanoelectromechanical systems, strain resilient electronics, multifunctional surfaces and reconfigurable quantum systems.