Mechanical exfoliation of non-layered metal oxides into ultrathin flakes

The exfoliation of layered crystals can produce diverse two-dimensional (2D) materials and heterostructures. However, the micromechanical cleavage of non-stratified materials into 2D flakes remains challenging due to z-direction consecutive bonding. Here we report a mechanical exfoliation method for producing freestanding 2D metal oxide flakes. By synchronizing the thermal decomposition of metal salts and water-assisted forming, we synthesize large-aspect-ratio lamellae of amorphous and crystalline metal oxides as parent materials, which can exfoliate to ultrathin flakes. The freestanding, transferrable features allow the room temperature integration of high-k metal oxide flakes as top-gate dielectrics in 2D material transistors. We utilize the dual-function Cr-doped AlO_x flake as the gating dielectric and component, sensing and storing the visible light by photon-programming floating gate effect, showing an in-sensor computing device. Our results provide a platform to investigate the fundamental properties of ultrathin metal oxides free of substrate clamping and pave the way to metal oxides-based functional devices. (Figure presented.).