Study of structural properties and defects of Ni-doped SnO₂ nanorods as ethanol gas sensors

An ethanol gas sensor with enhanced sensor response was fabricated using Ni-doped SnO₂ nanorods, synthesized via a simple hydrothermal method. It was found that the response (R = R ₀/R _g) of a 5.0 mol% Ni-doped SnO₂ (5.0Ni:SnO₂) nanorod sensor was 1.4 × 10⁴ for 1000 ppm C₂H₅OH gas, which is about 13 times higher than that of pure SnO₂ nanorods, (1.1 × 10³) at the operating temperature of 450 °C. Moreover, for 50 ppm C₂H₅OH gas, the 5.0Ni:SnO₂ nanorod sensor still recorded a significant response reading, namely 2.0 × 10³ with a response time of 30 s and recovery time of 10 min. To investigate the effect of Ni dopant (0.5-5.0 mol%) on SnO₂ nanorods, structural characterizations were demonstrated using field emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy and an ultraviolet-visible spectrometer. XRD results confirmed that all the samples consisted of tetragonal-shaped rutile SnO₂ nanorods. It was found that the average diameter and length of the nanorods formed in 5.0Ni:SnO₂ were four times smaller (∼6 and ∼35 nm, respectively) than those of the nanorods formed in pure SnO₂ (∼25 and 150 nm). Interestingly, both samples had the same aspect ratio, ∼6. It is proposed that the high response of the 5.0Ni:SnO₂ nanorod sensor can be attributed to the particle size, which causes an increase in the thickness of the charge depletion layer, and the presence of oxygen vacancies within the matrix of SnO₂ nanorods.