Growth-Mode Engineering of Epitaxial TiO₂ Thin Films for Room-Temperature Hydrogen Sensing and Battery Safety

Achieving reliable hydrogen sensing at room temperature remains a critical challenge due to the limited carrier transport and unstable surface chemistry of conventional polycrystalline oxides. Here, we demonstrate that precise growth-mode control of epitaxial anatase TiO₂ thin films via sputtering atmosphere engineering provides an effective route to overcoming these limitations. By systematically tuning the Ar/O₂ ratio, the TiO₂ growth mode transitions from a defective island-like mode to a layer-by-layer mode and finally to a stress-induced island. The film deposited at an 8/1 Ar/O₂ ratio achieves an ideal combination of perfect crystallinity, an atomically flat surface, and a balanced oxygen vacancy concentration, yielding a clean and well-defined Pd-TiO₂ interface upon catalyst deposition. The resulting Pd/TiO₂ sensor exhibits exceptional room-temperature hydrogen sensing performance: a strong response of 11.34 to 100 ppm of H₂, a low detection limit (5 ppm), excellent selectivity over other battery abuse gases, remarkable humidity resistance, and long-term stability. Comprehensive structural and mechanistic analyses reveal that the superior performance originates from an efficient interface-dominated sensing mechanism, rather than the conventional surface reaction pathway. This work establishes a "structure over stoichiometry" paradigm for developing advanced gas sensors and provides an effective route toward high-reliability, low-power hydrogen safety monitoring.