Piezostrain-Driven Bidirectional Enhancement of Optical Synaptic Plasticity in Wafer-Scale Co-Phased Tin Selenide Layers

Tin (Sn)-based two-dimensional (2D) materials exhibit intriguing mechanical and optoelectrical properties owing to their non-centrosymmetric crystallinity and tunable band structures. A judicious integration of these individually decoupled properties is projected to introduce unparalleled functionalities into them, which remain largely unexplored. Herein, we develop wafer-scale tin selenide (SnSe_2-<i>x</i>, 0 < <i>x</i> < 1) 2D layers composed of thermodynamically stable coexisting phases of SnSe and SnSe₂ with distinct functionalities and identify a strong interplay between their mechanical and optoelectrical characteristics. Mechanically, they display a strain-dependent piezoelectricity upon an anisotropic deformation of convex vs concave bending. Optoelectrically, they present an optical pulse-induced potentiation and synaptic plasticity accompanying a wavelength-tunable photoconduction upon visible to near-infrared (IR) illuminations. Harnessing these two independent features in a coupled manner enables a drastic enhancement of their synaptic responsiveness by >40% with a piezostrain of <1%. These findings suggest opportunities for atomically thin semiconductors in mechano-optical neuromorphic device applications.