  The coupling of mechanical deformation and electrical stimuli at the
nanoscale has been a subject of intense investigation in the realm of materials
science. Recently, twisted van der Waals (vdW) materials have emerged as a
platform to explore exotic quantum states. These states are intimately tied to
the formation of moir\'e superlattices, which can be visualized directly
exploiting the electromechanical response. However, the origin of the response,
even in twisted bilayer graphene (tBLG), remains unsettled. Here, employing
lateral piezoresponse force microscopy (LPFM), we investigate the
electromechanical responses of marginally twisted graphene moir\'e
superlattices with different layer thicknesses. We observe distinct LPFM
amplitudes and spatial profiles in tBLG and twisted monolayer-bilayer graphene
(tMBG), exhibiting effective in-plane piezoelectric coefficients of 0.05 pm/V
and 0.35 pm/V, respectively. Force tuning experiments further underscore a
marked divergence in their responses. The contrasting behaviors suggest
different electromechanical couplings in tBLG and tMBG. In tBLG, the response
near the domain walls is attributed to the flexoelectric effect, while in tMBG,
the behaviors can be comprehended within the context of piezoelectric effect.
Our results not only provide insights to electromechanical and corporative
effects in twisted vdW materials with different stacking symmetries, but may
also show their potential for engineering them at the nanoscale.
