Nanostructured Indium Oxide Thin Films as a Room Temperature Toluene Sensor

Sunil Gavaskar Dasari; Pothukanuri Nagaraju; Vijayakumar Yelsani; Sreekanth Tirumala; Ramana Reddy M V

doi:10.1021/acsomega.1c01831

Nanostructured Indium Oxide Thin Films as a Room Temperature Toluene Sensor

ACS Omega. 2021 Jul 1;6(27):17442-17454. doi: 10.1021/acsomega.1c01831. eCollection 2021 Jul 13.

Authors

Sunil Gavaskar Dasari¹, Pothukanuri Nagaraju², Vijayakumar Yelsani³, Sreekanth Tirumala⁴, Ramana Reddy M V¹

Affiliations

¹ Thin Films & Nanomaterials Research Laboratory, Department of Physics, Osmania University, Hyderabad, Telangana State 500 007, India.
² Nanosensor Research Laboratory, Department of Physics, CMR Technical Campus, Kandlaokoya, Hyderabad, Telangana State 501 401, India.
³ Department of Physics, Anurag University, Hyderabad, Telangana State 500 088, India.
⁴ Department of Physics, JNTUH College of Engineering Jagtial, Nachupally (Kondagattu), Jagtial Dist, Telangana State 505 501, India.

Abstract

Toluene gas is the most toxic and affects the respiratory system of humans, and thereby, its detection at lower levels is an important task. Herein, we report a room temperature-operatable indium oxide-based chemiresistive gas sensor, which detects 50 ppm toluene vapors. Nanocrystalline indium oxide (In₂O₃) films were sprayed on a pre-cleaned glass substrate using a cost-effective spray pyrolysis method at different substrate temperatures in the range of 350-500 °C. The X-ray diffraction studies confirmed that the sprayed thin films, which were deposited at different substrate temperatures, exhibit a cubic structure. The preferred orientation was aligned along the (222) orientation. Average crystallite size calculation based on the Scherrer formula indicates that the crystallite size increases with the enhancement of substrate temperature. FESEM analysis showed that the indium oxide thin films possess uniform grain distribution, which persists over the entire substrate. As the substrate temperature is increased, a partial agglomeration in the film morphology was observed. The deposited film's nanostructured nature was confirmed by transmission electron microscopy, and the polycrystalline nature was confirmed from the selected area electron diffraction pattern. Root mean square roughness of the samples was determined from the atomic force microscopy studies. From the Raman spectra, characteristic vibrational modes appeared at 558.61, 802.85, and 1097.18 cm^-1 in all the samples, which confirms the cubic structure of indium oxide thin films. Photoluminescence emission spectra have been recorded with an excitation wavelength of 280 nm. The optical band gap was measured using the Tauc plot. The band gap was found to decrease with an increase in the substrate temperature. The gas-sensing performance of indium oxide films sprayed at various substrate temperatures has demonstrated a better response toward 50 ppm toluene gas at room temperature with good stability, and the response and recovery times were determined using a transient response curve.