Synthesis of single-crystal SnO2 nanowires for NOx gas sensors application

Abstract Single-crystal SnO 2 nanowires (NWs) were successfully synthesized and characterized as sensing materials for long-term NO x stability detection in environmental monitoring. Reproducible and selective growths of the SnO 2 NWs on a patterned, 5 nm-thick gold catalyst coated on a SiO 2 /Si wafer as substrate were conducted by evaporating SnO powder source at 960 °C in a mixture of argon/oxygen ambient gas (Ar: 50 sccm/O 2 : 0.5 sccm). The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman scattering, and photoluminescence (PL). The SEM and HRTEM images revealed that the products are single-crystal SnO 2 NWs with diameter and length ranges of 70 nm–150 nm and 10 μm–100 μm, respectively. The three observed Raman peaks at 476, 633, and 774 cm −1 indicated the typical rutile phase, which is in agreement with the XRD results. The NWs showed stable PL with an emission peak centered at around 620 nm at room-temperature, indicating the existence of oxygen vacancies in the NW samples. The electrical properties of synthesized SnO 2 NWs sensor were also investigated and it exhibited a negative temperature coefficient of resistance in the measured range (300–525 K). The calculated activation energy E c of SnO 2 NWs was 0.186 eV. Moreover, the SnO 2 NW sensors exhibited good response to NO x gas. The response of the sensors to 5 ppm NO x reached 105% at an operating temperature of 200 °C.