Precise preparation of α-Fe2O3/SnO2 core-shell nanowires via atomic layer deposition for selective MEMS-based H2S gas sensor

Heterostructured α-Fe2O3/SnO2 core-shell nanowires (NWs) are successfully synthesized assisted with atomic layer deposition (ALD). The gas sensing properties of α-Fe2O3/SnO2 core-shell NWs with various shell thicknesses in the range of 5–28 nm are investigated. The gas sensing mechanism is fully analyzed based on both the widely accepted electron depletion model and the Debye length concept. When the shell thickness reaches ∼18 nm, the sensor of the heterostructured α-Fe2O3/SnO2 core-shell NWs exhibit high responses (Ra/Rg) of 4.3 towards 10 ppm and 1.5 towards 1 ppm H2S at 250 °C, excellent selectivity, remarkable repeatability, and long-term stability of at least 3 months, which completely exceed that of pristine α-Fe2O3 NWs. The formation of α-Fe2O3/SnO2 heterojunction contributes to the effectively enhanced performance, which is further investigated and confirmed by density functional theory calculations. In addition, the sensors are fabricated based on specially designed MEMS sensing devices, providing excellent heating conditions for sensitive nanomaterials with the merits of low power consumption and high integration.