Shape-dependent in-plane piezoelectric response of SnSe nanowall/microspheres

Highlights: • Large-scale, crystalline SnSe nanowall/µ-spheres grown on flexible conductive wires. • Robust piezoelectricity (19.9 pm V^-1) of SnSe nanowall overcomes the monolayer limit. • Shape, position, frequency-dependent piezoelectric response shows antiparallel domains. • Switchable polar domains, butterfly amplitude curves confirm ferroelectricity of SnSe. • WT-SnSe nanowall-PNG device used to harness, monitor biomechanical human finger force. Group-IV monochalcogenides (MCs) belong to a noncentrosymmetric C_2v point group, have gained immense interest due to their semiconducting-electromechanical coupling behavior. Large polarization predicted in the armchair, zigzag directions of monolayer MCs leads to giant piezoelectricity than the other two-dimensional MX₂ (M = metal, and X = S, Se, Te) compounds. Herein, we report the discovery of shape, size-dependent piezoelectric response of SnSe nanowall (NWs)/µ-spheres using a driving frequency-dependent piezoelectric force microscopy approach. The robust, high in-plane piezoelectric coefficient of ≈ 19.9 pm V^-1 achieved for few-layered SnSe NWs (average width ≈35 nm), which overcomes the monolayer piezoelectricity limit in SnSe and odd/even layer combinations. The NWs/µ-spheres exhibited traditional butterfly-shaped amplitude curves, polar domains with a 180° phase shift confirmed the in-plane ferroelectric nature. Energy conversion, monitoring of human finger bending angles (30°, 60°, and 90°) was demonstrated by wire-type SnSe NW-based piezoelectric nanogenerator. Overall, the current study shows a large-scale homogeneous growth of highly crystalline MCs on flexible conductive wires by a one-pot solution-mediated process. This process will facilitate the fabrication of nanoscale piezoelectric/ferroelectric devices for neuromorphic computing, field-effect transistors, micro-power sources, and flexible medical electronic systems.