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<p>In the present study, the optical and gas-sensing properties of pure and Cr-doped SnO<sub>2</sub> thin films were investigated. A polycrystalline tetragonal crystal structure was observed in all deposited films, with a fundamental orientation peak along the (110) direction, as confirmed by X-ray diffraction studies. Atomic force microscopy was used to examine the surface morphology and surface roughness. Raman spectroscopy studies revealed that all the films exhibited three fundamental Raman modes of vibration at 474, 628, and 774&#xa0;cm-1, corresponding to the E<sub>g</sub>, A<sub>1g</sub>, and B<sub>2g</sub> modes, respectively. The electronic states of the deposited films are Sn<sup>4+</sup>, O<sup>2−</sup>, and Cr<sup>3+</sup>, confirmed using X-ray photoelectron spectroscopy (XPS). The average optical transmittance is above 78% for all Cr-doped SnO<sub>2</sub> thin films in the visible region. The optical band gap energy (<i>E</i><sub><i>g</i></sub>) was found to be decreased from 3.84&#xa0;eV for pure SnO<sub>2</sub> to 3.65&#xa0;eV in 3 at% Cr: SnO<sub>2</sub> film, whereas a slight increase of 3.72&#xa0;eV was observed in 5 at% Cr: SnO<sub>2</sub>. The gas-sensing properties of deposited films were investigated for various VOC gases and gas concentrations. The 3 at% Cr: SnO₂ thin film exhibited remarkable reactivity to isopropanol at 225&#xa0;°C, demonstrating exceptional selectivity, stability, and rapid reaction and recovery durations of 9&#xa0;s and 11&#xa0;s, respectively, for 20&#xa0;ppm of isopropanol. Further, the possible gas sensing mechanism of Cr-doped SnO<sub>2</sub> thin films to isopropanol is investigated.</p>

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Tailored optical band gap of Cr-doped SnO2 thin films for improved isopropanol gas sensing

  • 期刊论文

  • 发表日期：

    2026年1月9日

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  • Harish Sharma Akkera,
  • Madhukar Poloju,
  • Paramita Sarkar,
  • Nagaiah Kambhala,
  • Anna Mallikarjun

摘要

In the present study, the optical and gas-sensing properties of pure and Cr-doped SnO2 thin films were investigated. A polycrystalline tetragonal crystal structure was observed in all deposited films, with a fundamental orientation peak along the (110) direction, as confirmed by X-ray diffraction studies. Atomic force microscopy was used to examine the surface morphology and surface roughness. Raman spectroscopy studies revealed that all the films exhibited three fundamental Raman modes of vibration at 474, 628, and 774 cm-1, corresponding to the Eg, A1g, and B2g modes, respectively. The electronic states of the deposited films are Sn4+, O2−, and Cr3+, confirmed using X-ray photoelectron spectroscopy (XPS). The average optical transmittance is above 78% for all Cr-doped SnO2 thin films in the visible region. The optical band gap energy (Eg) was found to be decreased from 3.84 eV for pure SnO2 to 3.65 eV in 3 at% Cr: SnO2 film, whereas a slight increase of 3.72 eV was observed in 5 at% Cr: SnO2. The gas-sensing properties of deposited films were investigated for various VOC gases and gas concentrations. The 3 at% Cr: SnO₂ thin film exhibited remarkable reactivity to isopropanol at 225 °C, demonstrating exceptional selectivity, stability, and rapid reaction and recovery durations of 9 s and 11 s, respectively, for 20 ppm of isopropanol. Further, the possible gas sensing mechanism of Cr-doped SnO2 thin films to isopropanol is investigated.