Stochastic Stress Jumps Due to Soliton Dynamics in Two-Dimensional van der Waals Interfaces

Abstract

The creation and movement of dislocations determine the nonlinear mechanics of materials. At the nanoscale, the number of dislocations in structures become countable, and even single defects impact material properties. While the impact of solitons on electronic properties is well studied, the impact of solitons on mechanics is less understood. In this study, we construct nanoelectromechanical drumhead resonators from Bernal stacked bilayer graphene and observe stochastic jumps in frequency. Similar frequency jumps occur in few-layer but not twisted bilayer or monolayer graphene. Using atomistic simulations, we show that the measured shifts are a result of changes in stress due to the creation and annihilation of individual solitons. We develop a simple model relating the magnitude of the stress induced by soliton dynamics across length scales, ranging from <0.01 N/m for the measured 5 μm diameter to ∼1.2 N/m for the 38.7 nm simulations. These results demonstrate the sensitivity of 2D resonators are sufficient to probe the nonlinear mechanics of single dislocations in an atomic membrane and provide a model to understand the interfacial mechanics of different kinds of van der Waals structures under stress, which is important to many emerging applications such as engineering quantum states through electromechanical manipulation and mechanical devices like highly tunable nanoelectromechanical systems, stretchable electronics, and origami nanomachines.

Dissipation from Interlayer Friction in Graphene Nanoelectromechanical Resonators

“…60 The presence of the ripples in the BS-BL resonators are consistent with kink and antikink defect rising from local stacking faults known as solitons. 60 The competition between in-plane strain, stacking-fault energy, and bending result in the buckled geometry that is seen in the BS-BL membranes but not in the monolayer or twisted samples. A challenge of 2D resonators and NEMS in general is that they are sensitive to variations in pretension, surface contaminants, added mass, potential grain boundaries, clamping, and membrane morphology, which lead to large and difficult to control device-to-device variations in dissipation and frequency.…”

“…To fabricate the 2D drumhead resonators, we transfer and suspend 2D atomic membranes composed of twisted bilayer graphene (T-BL), Bernal-stacked bilayer graphene (BS-BL), and monolayer graphene (ML) over arrays of circular holes with 5 μm diameter and 250 nm depth in a 285 nm thick silicon oxide layer on a degenerately doped silicon substrate. 60 We electrically contact the transferred layer by evaporating Cr/Au 5/40 nm through a shadow mask. We use chemical vapor deposition grown graphene, which results in bilayer patches 20−40 μm in size on a continuous monolayer.…”

“…In this plot, the frictionless bilayer quality factor is assumed to be Q 0 = 44.4, the amplitude of motion at the midpoint is 0.2 nm, and the range of prestrains spans the values previously measured by our group and others on devices with the same geometry and fabrication steps. 60 The horizontal bands on the plot compare the average quality factors for the two bilayer cases, twisted (green) and Bernal stacked (red). As a comparison, the shaded yellow region shows the range of interlayer frictions measured statically in graphite interfaces, 72 along with the average of σ f = 1.1 × 10 −3 N/m (dashed orange line).…”

“…One particular mystery in 2D resonators is that the measured quality factors do not significantly improve as thickness increases to a few layers , against expectations from theoretical scaling laws. This suggests that there are additional mechanisms of dissipation in multilayer 2D materials, occurring as a result of the weak bonding and out of plane shear modulus of the van der Waals interface. − For instance, in the elastic regime, Raman spectroscopy of stacked 2D layers show ultralow frequency Terahertz shear modes. , Beyond the elastic regime, plastic slip between aligned layers leads to mobile stacking faults called solitons, which glide through the interface. − In twisted multilayers or heterostructures, the misalignment between layers leads to a moiré superlattice with no stable equilibrium for most angles and structural lubricity. , What is not yet studied or understood is how the interlayer friction observed in previous measurements will affect the dynamic dissipation in 2D NEMS.…”

“…Figure b shows an optical image of a typical resonator from twisted bilayer graphene. To fabricate the 2D drumhead resonators, we transfer and suspend 2D atomic membranes composed of twisted bilayer graphene (T-BL), Bernal-stacked bilayer graphene (BS-BL), and monolayer graphene (ML) over arrays of circular holes with 5 μm diameter and 250 nm depth in a 285 nm thick silicon oxide layer on a degenerately doped silicon substrate . We electrically contact the transferred layer by evaporating Cr/Au 5/40 nm through a shadow mask.…”