V.V. Ganbavle

Nitrogen dioxide sensing properties of sprayed tungsten oxide thin film sensor: Effect of film thickness

We report a study on effect of film thickness on NO2 sensing properties of sprayed WO3 thin films. WO3 thin films varying in thicknesses are deposited onto the glass substrates by simple spray pyrolysis technique by varying the volume of spray solution.Thin film gas sensors are characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) techniques to study their physical properties. Film having thickness 745nm has shown highest gas response of 97% with 12 and 412s response and recovery times, respectively towards 100ppm NO2 concentration. Gas response of 20% is observed towards 10ppm NO2 at 200°C operating temperature. Sensitivity of the optimal sensor is 0.83%/ppm when operating at 200°C with 10ppm lower detection limit. The response of the sensor is reproducible and WO3 films are highly selective towards NO2 in presence of mist of various interfering gases viz. H2S, NH3, LPG, CO and SO2.

Multifunctional zinc oxide thin films for high-performance UV photodetectors and nitrogen dioxide gas sensors

In order to find new approaches for sensor devices; ZnO based gas sensors and UV photodetectors with higher sensitivity and responsivity were fabricated. ZnO thin films were synthesized by using inexpensive successive ionic layers by an adsorption and reaction method (SILAR) on the amorphous glass substrate. The fabricated metal���semiconductor–metal (MSM) UV photoconductive detector shows excellent photoresponse with fast response and recovery times (18 s and 24 s) under UV illumination (wavelength −365 nm and power density −1.8 μW cm−2) at 5 V bias voltage. The detector shows an ohmic nature between metal semiconductor contacts with spectral responsivity 185 A W−1. Gas sensing performance for detecting NO2 gas was studied at a relatively low operating temperature of 175 °C and 20.52 response was observed for the optimized film for a 60 ppm gas concentration. The sensor has good repeatability along with a quick response time, whereas it has a relatively high recovery time. The sensor is highly selective towards NO2 gas as compared to other gases, and has a lower detection limit of 10 ppm at an operating temperature of 175 °C. The present study opens up possibilities for the extensive study of ZnO thin film based sensor devices using a simple chemical deposition method (SILAR).

Effect of Substrate Temperature on the Properties of Sprayed WO3 Thin Films Using Peroxotungstic Acid and Ammonium Tungstate: A Comparative Study

A comparative study on the physicochemical properties of tungsten oxide (WO3) thin films synthesized using peroxotungstic acid (PTA) and ammonium tungstate (AT) by simple spray pyrolysis technique is reported. X-ray diffraction patterns show that the films deposited using both the precursors are polycrystalline with monoclinic crystal structure. The x-ray photoelectron spectroscopy studies confirm that the films are sub-stoichiometric with O/W ratios of 2.93 and 2.87, respectively, for typical PTA and AT films. Tungsten (W) exists in two chemical states, 5+ and 6+. Scanning electron microscopy images show the uniform and dense network of wires in PTA films, while the films deposited using AT possess a porous structure with small grains. Electrical and dielectric studies show that films are highly resistive and possess high dielectric constant. The near ultra-violet, blue, green and weak red emissions due to defects were observed in the photoluminescence studies. Properties of the WO3 thin films reported here are suitable for gas sensor applications. Films deposited using PTA are more functional than those deposited using AT.

Regular ArticleAssessment of structural, morphological, magnetic and gas sensing properties of CoFe2O4 thin films

Polycrystalline CoFe2O4 thin films are deposited onto the quartz substrates by spray pyrolysis technique. Rietveld refinement analysis confirmed the films are polycrystalline in nature with spinel cubic crystal structure. Rietveld refinement analysis was employed to estimate the cation distribution in spinel lattice sites. Surface micrographs shows the granular morphology with average grain size decreases with increase in solution concentration. The presence of two characteristic absorption bands around 579 and 391cm-1 in the FTIR study confirms the formation of single phase CoFe2O4. Vibrating sample magnetometer measurement confirmed the predominant ferrimagnetic nature of thin films which confirms the maximum saturation magnetization with moderate coercivity was useful for making effective gas sensor. The gas response towards different operating temperatures, gas concentrations and solution concentrations was systematically studied. The films show the maximum gas response 70% at 0.1M solution concentration at 150°C operating temperature. The films are well selective towards NO2 as compared with other test gases with good reproducibility.