Revealing stacking order transition via nanomechanical resonator

The physical properties of two-dimensional (2D) van der Waals (vdW) materials are profoundly influenced by their stacking orders, which affect interlayer coupling and crystal symmetry, leading to fascinating strongly correlated orders. Detecting stacking orders is important, yet challenging as they involve sub-nanometer shifts in the relative arrangement of layers. In this study, we utilize nanomechanical resonators to detect the strain change during the stacking order transition of octahedrally coordinated thin molybdenum ditelluride (MoTe2) membranes and show the change in stacking orders can be reflected by the vibration modes of nanomechanical resonators. We discover that a strain as small as 0.014%—induced by transitions in the stacking order—results in a notable frequency shift up to 1.019 MHz in the mechanical resonance. We establish the relationship between the detection sensitivity of stacking orders and both internal and external parameters including higher-order vibrations, electrostatic energy, and initial strain. Our nanomechanical methodology offers a potential avenue for creating a comprehensive phase diagram by uncovering stacking orders across a wide array of van der Waals materials and leveraging ultralow-barrier stacking order transitions for energy-efficient devices.