Nanoscale strain in 2D materials from coupled structural phase transformations in BiFeO₃

2D materials may be coupled to thin films of multiphase BiFeO₃ (BFO), where electric-field induced transformations between the BFO rhombohedral (R) and tetragonal (T) structural phases can generate a large amount of strain in a coupled 2D system. Therefore, this platform allows for dynamic, high magnitude, electrically gateable strain to be generated in 2D materials that is robust to low temperatures. Here, we show that 1T’-MoTe₂ and 2H-MoS₂ can be coupled to strain induced by BFO structural phase transformations. Thin film BiFeO₃/La_0.7Sr_0.3MnO₃ heterostructures are grown on LaAlO₃ substrates to stabilize the mixed phase growth, and TMDC materials or van der Waals heterostructures are transferred onto the oxide thin film surface. Conductive atomic force microscopy (C-AFM) is used for application of out-of-plane electric field onto individual flakes. We find that TMDC flake thickness impacts adhesion and conformality to structural transformations in BFO: 1T’-MoTe₂ is fully conformal to C-AFM induced structural changes in BFO when flake thicknesses are below 3 nm. We demonstrate that bare and hBN-capped monolayer MoS₂ can be strained with BFO, where photoluminescence spectroscopy on MoS₂ shows variations in strain that are correlated with C-AFM induced structural transformations.