In₂O₃-Modified ZnO@SnO₂ Core–Shell Nanosheets for Ethanol Sensing

The In 2 O 3 -modified ZnO@SnO 2 core–shell nanosheets (NSs) were synthesized via an innovative and facile route that combines the modified hydrothermal method with an atomic layer deposition (ALD) process. The self-limiting reactions inherent to ALD facilitate precise control over the film thickness, enabling the design of well-defined core–shell nanostructures for gas-sensing applications. Evaluation of gas-sensing properties revealed that the construction of the ZnO@SnO 2 core–shell heterostructure combined with In 2 O 3 surface modification markedly improved the sensing performance. The optimized ZnO@SnO 2 /In 2 O 3 sensor with a 20 nm SnO 2 shell (denoted as Z@S/I-20) exhibited a high response ( R a / R g = 148.6) toward 100 ppm ethanol at 350 °C, which was approximately 3.6 and 1.6 times higher than that of ZnO/In 2 O 3 NSs (40.3) and unmodified ZnO@SnO 2 core–shell NSs with 20 nm SnO 2 (91.6), respectively. Furthermore, the Z@S/I-20 gas sensor demonstrated a response/recovery time of 140.2:36.6 s, remarkable selectivity toward ethanol, and an ultralow detection limit of 64 ppb. The significantly enhanced sensing performance is attributed to the synergistic effect of heterojunction formation, the porous mesh morphology of In 2 O 3 nanowires, and the optimized SnO 2 shell thickness, as systematically discussed in this work. These findings highlight the potential of the proposed synthesis route and sensor design for the development of high-performance microelectromechanical system (MEMS)-based gas sensors that can be applied to ethanol detection.