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<p>Cd-doped SnO₂ thin films were deposited by nebulizer spray pyrolysis and systematically investigated for their structural, optical, morphological, and gas sensing characteristics. X-ray diffraction confirmed the tetragonal rutile phase with crystallite sizes in the range of 65–76&#xa0;nm. Optical transmission studies showed a direct band gap between 4.11 and 4.07&#xa0;eV, with slight variations due to Cd incorporation. Surface morphology observed by FESEM revealed that doping strongly influenced grain structure: while pure SnO₂ exhibited compact grains, the 3 wt% Cd-doped film displayed a chain-like nanostructure with enhanced porosity and uniform grain distribution. Gas sensing measurements demonstrated that the 3 wt% Cd-doped film exhibited the best response toward NH₃ at room temperature, with a gas response of 1470 % for 250 ppm, a rapid response time of 6.5&#xa0;s, and a recovery time of 9.1&#xa0;s. The improved sensing properties were attributed to the synergy between Cd-induced oxygen vacancies, increased surface area, and the chain-like morphology, which provided abundant active sites for adsorption. Furthermore, the sensor’s response was strongly influenced by relative humidity. Higher RH levels facilitated water dissociation into hydroxyl groups, which interacted with adsorbed oxygen species and enhanced NH₃ adsorption, leading to a monotonic increase in response. These results demonstrate that controlled Cd doping optimizes the structure and surface chemistry of SnO₂ thin films, making the 3 wt% composition a promising candidate for room-temperature ammonia detection in humid environments.</p>

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High-sensitivity NH₃ sensors based on spray-pyrolyzed cadmium-modified tin oxide thin films

  • 期刊论文

  • 发表日期：

    2025年12月22日

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  • Mahalingam Sakthivel Revathy,
  • Rajan Jansi,
  • Lakshmanan Muthulakshmi,
  • Arokia Anto Jeffery,
  • Vanga Ganesh,
  • Majahar Hussain Mahammd

摘要

Cd-doped SnO₂ thin films were deposited by nebulizer spray pyrolysis and systematically investigated for their structural, optical, morphological, and gas sensing characteristics. X-ray diffraction confirmed the tetragonal rutile phase with crystallite sizes in the range of 65–76 nm. Optical transmission studies showed a direct band gap between 4.11 and 4.07 eV, with slight variations due to Cd incorporation. Surface morphology observed by FESEM revealed that doping strongly influenced grain structure: while pure SnO₂ exhibited compact grains, the 3 wt% Cd-doped film displayed a chain-like nanostructure with enhanced porosity and uniform grain distribution. Gas sensing measurements demonstrated that the 3 wt% Cd-doped film exhibited the best response toward NH₃ at room temperature, with a gas response of 1470 % for 250 ppm, a rapid response time of 6.5 s, and a recovery time of 9.1 s. The improved sensing properties were attributed to the synergy between Cd-induced oxygen vacancies, increased surface area, and the chain-like morphology, which provided abundant active sites for adsorption. Furthermore, the sensor’s response was strongly influenced by relative humidity. Higher RH levels facilitated water dissociation into hydroxyl groups, which interacted with adsorbed oxygen species and enhanced NH₃ adsorption, leading to a monotonic increase in response. These results demonstrate that controlled Cd doping optimizes the structure and surface chemistry of SnO₂ thin films, making the 3 wt% composition a promising candidate for room-temperature ammonia detection in humid environments.