SnO₂–CuO–ZnO nanostructured thin films were synthesized using the gel spin-coating method and systematically optimized by varying the wt% ratio (90:5:5, 80:10:10, 70:15:15, 60:20:20). A range of characterization techniques was employed to assess the structural, optical, electrical, and sensing properties of the synthesized thin films. The techniques include X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS-Elemental-Mapping), photoluminescence (PL), UV-vis measurements, Hall effect measurements, and sensitivity measurements. Structural XRD, Raman and morphological (FE-SEM/AFM) analyses confirmed the co-existence of rutile SnO2, tenorite CuO, and ZnSnO3 phases with rough, nearly spherical nanostructured porosity, while XPS and EDS mapping analyses validated the expected oxidation states of Sn4+, Cu2+, Zn2+, and O2− and revealed an oxygen-vacancy fraction of ~ 33–38% that governs adsorption–desorption kinetics. Optical studies revealed band gaps ranging from 3.82 to 4.36 eV, and photoluminescence analysis indicated the presence of oxygen vacancy defects. Hall effect measurements demonstrated a significant enhancement in charge carrier mobility, from 3.28 cm²/V s to 108 cm2/V s, which correlated with improved gas sensing performance. In terms of gas sensing, at room temperature, the deposited films showed sensitivities of 57.1% for NO2, 81.5% for H2S, and 60.7% for NH3, with response times of 31.5s, 16.2s, and 11.7s, respectively. At 100 °C, sensitivities increased to 68.8% for NO2, 91.4% for H2S, and 38.2% for NH3, while response times decreased to 9s, 6.3s, and 9.9s. The highest sensitivity was observed at 200 °C, where the films achieved 91.7% for NO2, 90.2% for H2S, and 39.4% for NH3, with response times of 4.5s, 8.1s, and 7.2s, respectively. Calibration plots enabled multi-gas sensing, revealing pronounced detection limits and selectivity: 57% for NO₂ (86 ppm), 46% for H₂S (12.6 ppm), and 17% for NH₃ (11.9 ppm). In contrast, weakly polar VOCs (toluene, xylene, isopropanol) produced responses below 3.5%. Repeatability tests over ≥ 4 cycles yielded relative standard deviations below 3%, and stability analysis after eight months of ambient storage retained > 90% of the original response. The optimized 90:5:5 film exhibited a humidity response of 52.46%, with response and recovery times of 2 and 3 s, respectively, and negligible hysteresis at room temperature. The findings establish that coupling oxygen-vacancy chemistry with p–n–n heterojunction engineering in ternary SnO–CuO–ZnO films yields fast, selective, and stable multi-gas and humidity sensing at room temperature.

Design and characterization of Sn-Cu-Zn multi-cation metal oxide nanostructures for enhanced humidity and multi-gas sensing applications

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发表日期：

2026年1月23日

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Karrar. Saad. Mohammed,
J. Al-Zanganawee,
Asaad A. Kamil,
Tahseen H. Mubarak

摘要

SnO₂–CuO–ZnO nanostructured thin films were synthesized using the gel spin-coating method and systematically optimized by varying the wt% ratio (90:5:5, 80:10:10, 70:15:15, 60:20:20). A range of characterization techniques was employed to assess the structural, optical, electrical, and sensing properties of the synthesized thin films. The techniques include X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS-Elemental-Mapping), photoluminescence (PL), UV-vis measurements, Hall effect measurements, and sensitivity measurements. Structural XRD, Raman and morphological (FE-SEM/AFM) analyses confirmed the co-existence of rutile SnO₂, tenorite CuO, and ZnSnO₃ phases with rough, nearly spherical nanostructured porosity, while XPS and EDS mapping analyses validated the expected oxidation states of Sn⁴⁺, Cu²⁺, Zn²⁺, and O²⁻ and revealed an oxygen-vacancy fraction of ~ 33–38% that governs adsorption–desorption kinetics. Optical studies revealed band gaps ranging from 3.82 to 4.36 eV, and photoluminescence analysis indicated the presence of oxygen vacancy defects. Hall effect measurements demonstrated a significant enhancement in charge carrier mobility, from 3.28 cm²/V s to 108 cm²/V s, which correlated with improved gas sensing performance. In terms of gas sensing, at room temperature, the deposited films showed sensitivities of 57.1% for NO₂, 81.5% for H₂S, and 60.7% for NH₃, with response times of 31.5s, 16.2s, and 11.7s, respectively. At 100 °C, sensitivities increased to 68.8% for NO₂, 91.4% for H₂S, and 38.2% for NH₃, while response times decreased to 9s, 6.3s, and 9.9s. The highest sensitivity was observed at 200 °C, where the films achieved 91.7% for NO₂, 90.2% for H₂S, and 39.4% for NH₃, with response times of 4.5s, 8.1s, and 7.2s, respectively. Calibration plots enabled multi-gas sensing, revealing pronounced detection limits and selectivity: 57% for NO₂ (86 ppm), 46% for H₂S (12.6 ppm), and 17% for NH₃ (11.9 ppm). In contrast, weakly polar VOCs (toluene, xylene, isopropanol) produced responses below 3.5%. Repeatability tests over ≥ 4 cycles yielded relative standard deviations below 3%, and stability analysis after eight months of ambient storage retained > 90% of the original response. The optimized 90:5:5 film exhibited a humidity response of 52.46%, with response and recovery times of 2 and 3 s, respectively, and negligible hysteresis at room temperature. The findings establish that coupling oxygen-vacancy chemistry with p–n–n heterojunction engineering in ternary SnO–CuO–ZnO films yields fast, selective, and stable multi-gas and humidity sensing at room temperature.