Nanostructured Indium Oxide Thin Films as a Room Temperature Toluene Sensor

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 (In 2 O 3 ) films were sprayed on a precleaned 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.

Synthesis of nano-crystallite gypsum and bassanite from waste Pila globosa shells: crystallographic characterization

“…Along with phase identification, crystallographic parameters such as the crystallite size, crystallinity index, lattice parameters, unit cell volume, dislocation density, and microstrain were estimated using eqn (4)–(10). 19–21 Both gypsum and bassanite are monoclinic crystals but have the different space groups of C 2/ c (15) and I 2 (5), respectively.In the above equations, β = full width at half maximum (FWHM) (in radian); Scherrer's constant K = 0.94; λ = X-ray source wavelength = 0.15406 nm; θ = angle of diffraction; a , b , c , and h , k , l = lattice parameters of crystals; H 1 = peak height of the three strongest peaks.…”

“…Along with phase identication, crystallographic parameters such as the crystallite size, crystallinity index, lattice parameters, unit cell volume, dislocation density, and microstrain were estimated using eqn (4)- (10). [19][20][21] Both gypsum and bassanite are monoclinic crystals but have the different space groups of C2/c (15) and I2 (5), respectively.…”

“…The average of three peaks model is associated with the crystallite size of three strong peaks, which is also based on the Scherrer equation. The mathematical expressions of this model are presented in eqn ( 19)- (21), and the details of the procedures are listed elsewhere. 32 Three strong peaks were considered to measure the average diffraction angle and peak broadening.…”

“…32 Three strong peaks were considered to measure the average diffraction angle and peak broadening. The average of the X-ray wavelength was also computed using eqn (21).…”

Effects of film thickness and annealing temperature on the properties of molybdenum carbide films prepared using pulsed direct-current magnetron sputtering

“…The film thickness was characterized using a step profiler (Bruker Nano, DektakXT) and X-ray reflectometry (XRR; PANalytical Empyrean). The phase structures of the films were characterized using XRD (PANalytical Empyrean), and the grain size was calculated according to the Scherrer formula [12]. XRD patterns were obtained using CuKα radiation (λ=0.154 nm), carried out at 40 mA and 40 kV, with a scanning angle range of 2θ=20°-90°and a scanning step size of 0.05°.…”