Heteroepitaxy of 2D MoO2 single crystals on A-plane sapphires for in-sensor edge computing

Two-dimensional (2D) non-layered oxides, such as MoO2, are emerging candidates for next-generation electronics, optoelectronics, and sensors, especially novel in-sensor computing. However, there is a lack of effective methods to grow large-area 2D MoO2 single crystals due to multiple preferred orientations induced by uncontrolled vertical growth. Here, we report a heteroepitaxial growth of unidirectionally aligned 2D MoO2 nanosheets on an A-plane sapphire substrate that has degenerated vertical symmetry to direct a uniaxial texture of monoclinic MoO2. This leads to 2D MoO2 single crystals covering >90% of an entire centimeter-scale A-sapphire substrate confirmed by second-harmonic generation mapping and selected-area electron diffraction. These high-quality 2D MoO2 nanosheets yield a unique memristive photodetector that exhibits tunable photocurrent corresponding to five programmable logic states. These programmable states are further utilized to construct an in-sensor edge computing system for image contrast enhancement, demonstrating the potential of epitaxial 2D non-layered oxides for artificial vision, Internet of Things, and other emerging applications.