Influence of Interfacial Stress on the Structural Characteristics and Hydrogen Sensing Performance of WO3 Films

Tungsten trioxide (WO3) exhibits complementary optical and electrical responses toward hydrogen, yet the interplay between interfacial stress, crystal phase stabilization, and gasochromic/chemiresistive performance remains insufficiently understood. In this work, WO3 films were grown on four single-crystal oxide substrates to systematically tune interfacial stress and thereby modulate the resulting crystal phase, microstructure, and exposed facets. θ–2θ diffraction revealed that WO3 adopts a monoclinic phase on YAlO3 and SrLaAlO4, whereas a high-temperature orthorhombic phase is stabilized on LaAlO3 (LAO) and SrTiO3 due to stronger interfacial constraint. Compared with the amorphous quartz reference, the single-crystal substrates significantly enhanced both gasochromic and chemiresistive responses. In particular, the orthorhombic WO3/LAO film exhibited an electrical response of 1.97 × 104 (Rair/RH2), an optical transmittance changed of 12.7%, and an electrical response time of 1 s toward 2% H2 at 80 °C, far exceeding the monoclinic and amorphous counterparts. The combined effects of stress-induced phase stabilization, film orientation, and hydrogen diffusion pathways are shown to govern the non-monotonic sensing trends among different substrates. These findings elucidate the structural origin of hydrogen sensitivity in WO3 and provide guidance for stress-engineered design of high-performance gasochromic and chemiresistive sensors.