Elastic Properties of BiOCl and Bi₃O₄Cl Freestanding Circular Membranes

Bismuth oxychlorides are emerging two-dimensional wide-bandgap semiconductors with exceptional potential for advanced photoelectric applications. Elastic strain engineering is a promising strategy to enhance their photoelectric performances. However, fundamental elastic properties of bismuth oxychlorides are largely unknown. In this work, atomic force microscopy based nanoindentations were employed to characterize sub 5 nm thick freestanding BiOCl and Bi₃O₄Cl circular membranes, and recorded elastic responses were analyzed using a nonlinear membrane model. Experimentally acquired Young's moduli and breaking strains of BiOCl and Bi₃O₄Cl membranes indicate a Cl-Cl interfacial shear effect in epitaxially grown BiOCl and a process-induced defect effect in the phase-transformed Bi₃O₄Cl. Built atomistic models illustrated bond strain behaviors of structurally symmetric BiOCl and asymmetric Bi₃O₄Cl and enabled predictions of strain-mediated interlayer electric fields and electronic structures. These results provide fundamental insights into the unique nanomechanics of layered bismuth oxychlorides and show guidelines of elastic strain engineering to tailor photoelectric properties of BiOCl and Bi₃O₄Cl.