Raman scattering of two-dimensional MoO2 flakes at high pressure

Two-dimensional (2D) MoO2, a binary nonlayered material, has been extensively studied for potential applications in catalysis and electronics. However, the preparation of 2D MoO2 remains challenging. Herein, we report the growth of 2D MoO2 flakes with rhombic morphology on the sapphire substrate via a chemical vapor deposition (CVD) method. Atomic force microscopy shows the CVD-grown MoO2 flakes with thin thickness. The CVD-obtained MoO2 with a stoichiometric ratio of 1:2 is verified using energy-dispersive X-ray spectroscopy. Scanning transmission electron microscopy (STEM) characterization reveals the high-quality, single-crystal nature of the CVD-derived 2D MoO2 flakes. The phonon vibration and structural transition of 2D MoO2 are investigated by temperature-dependent and high-pressure Raman spectra. This study paves the way for exploring the pressure-dependent properties of 2D MoO2.