Thermally driven oxidation and conductive-to-insulating transition of liquid-metal-printed gallium films for 2D...

Liquid-metal-derived oxide nanofilms have emerged as promising candidates for scalable electronic materials, yet the oxidation pathway governing their electrical functionality remains poorly understood. Here, we report a systematic study on the thermally driven oxidation behavior of liquid-metal-printed gallium films and its decisive role in inducing a conductive-toinsulating transition for two-dimensional (2D) electronics. Ultrathin gallium-based films were prepared through a dewetting-enabled printing process under ambient conditions, yielding smooth and transferable films with single-layer thicknesses of ~4.5 nm. The as-printed films exhibit partial surface oxidation while retaining residual metallic gallium, resulting in conductive vertical transport. Pure oxygen exposure at room temperature leads mainly to surface adsorption of oxygen species and fails to achieve complete oxidation. In contrast, thermal annealing in oxygen-containing atmosphere progressively converts metallic Ga into gallium oxide, as evidenced by X-ray photoelectron spectroscopy. High-temperature treatment further induces crystallization into polycrystalline β-Ga₂O₃, confirmed by X-ray diffraction and Raman spectroscopy. Consequently, the printed films undergo a pronounced conductive-to-insulating transition, exhibiting pA-level leakage current, and a dielectric constant of ~4.2. When integrated as gate dielectrics in back-gated MoS₂field-effect transistors, the devices deliver an on/off ratio of ~10⁶and a minimum subthreshold swing of 74 mV/dec. This work clarifies the thermal oxidation mechanism of liquid-metal-printed gallium films and establishes a scalable route toward functional dielectric layers for next-generation 2D electronics.