纳米尺度的机械变形和电刺激的耦合一直是材料科学领域的深入研究主题。最近,扭曲的范德华(vdW)材料已经成为探索奇异量子态的平台。这些状态与莫尔超晶格的形成密切相关,这可以通过直接利用机电响应来可视化。然而,回应的起源,即使在扭曲的双层石墨烯(TBLG)中,仍未解决。这里,采用横向压电响应力显微镜(LPFM),我们研究了不同层厚度的边际扭曲石墨烯莫尔超晶格的机电响应。我们观察到tBLG和扭曲单层双层石墨烯(tMBG)中不同的LPFM幅度和空间分布,表现出0.05和0.35pm/V的有效面内压电系数,分别。力调整实验进一步强调了他们的反应明显不同。对比行为表明tBLG和tMBG中的机电耦合不同。在tBLG中,畴壁附近的响应归因于挠曲电效应,而在tMBG,这些行为可以在压电效应的背景下理解。我们的结果不仅提供了对具有不同堆叠对称性的扭曲vdW材料中的机电和社团效应的见解,而且还可能提供一种在纳米级上进行工程的方法。
The coupling of mechanical deformation and electrical stimuli at the nanoscale has been the subject of intense investigation in the realm of materials science. Recently, twisted van der Waals (vdW) materials have emerged as a platform for exploring exotic quantum states. These states are intimately tied to the formation of moiré superlattices, which can be visualized by 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 moiré 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 and 0.35 pm/V, respectively. Force tuning experiments further underscored 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 the piezoelectric effect. Our results not only provide insights into electromechanical and corporative effects in twisted vdW materials with different stacking symmetries but may also offer a way to engineer them at the nanoscale.