Facile synthesis of nanostructured WO3 thin films and their characterization for ethanol sensing.

A simple technique to fabricate nanostructured WO3 thin films onto conductomeric transducers has been employed for ethanol sensing application. Initially, pure tungsten (W) thin films were deposited onto the substrate employing RF sputterer and followed by an etching process. Three types of etching agent were used: nitric (HNO3), sulphuric (H2SO4), and phosphoric (H3PO4) acid. It was found that the surface morphology and crystallinity of the WO3 films were heavily dependant to the etchants employed during the fabrication process. The developed sensors were tested towards ethanol vapor of different concentrations (10–200 ppm) at temperatures between room and 450 °C. The sensors showed stable and reproducible response at optimum operating temperatures. High sensor response towards vaporized ethanol as well as fast τres and τrec was observed during the “adsorption” and “desorption” interval. The recorded maximum response for these devices when exposed towards 100 ppm ethanol was measured to be 8 (Ro = 4.6 kΩ), 5.8 (Ro = 22.5 GΩ), and 5 (Ro = 0.29 MΩ) for HNO3, H3PO4, and H2SO4, respectively. The optimum operating temperatures were determined to be 400, 300–380, and 360 °C for the sensors developed using HNO3, H3PO4, and H2SO4, respectively

H2 and NO2 gas sensors with ZnO nanobelt layer on 36° LiTaO3 and 64° LiNbO3 SAW transducers

Single crystal nanobelts of ZnO were synthesized and deposited onto 36° YX LiTaO<sub>3</sub> and 64° YX LiNbO<sub>3</sub> surface acoustic wave (SAW) devices for gas sensing applications. Sensor response, defined as the change in resonant frequency, was measured for H<sub>2</sub> and NO<sub>2</sub> between 20 and 200°C. Measured sensor responses were 3.5 kHz towards 10 ppm NO<sub>2</sub> for a 64° LiNbO<sub>3</sub> SAW transducer operating at 160°C and 3 kHz towards 1% H<sub>2</sub> for a 36° LiTaO<sub>3</sub> SAW transducer operating at 185°C temperature

Titanium dioxide based 64° YX LiNbO3 surface acoustic wave hydrogen gas sensors

Amorphous titanium dioxide (TiO2) and gold (Au) doped TiO2-based surface acoustic wave (SAW) sensors have been investigated as hydrogen gas detectors. The nanocrystal-doped TiO2 films were synthesized through a sol-gel route,mixing a Ti-butoxide-based solution with diluted colloidal gold nanoparticles. The films were deposited via spin coating onto 64\ub0 YX LiNbO3 SAWtransducers in a helium atmosphere. The SAW gas sensors were operated at various temperatures between 150 and 310 \ub0C. It was found that gold doping on TiO2 increased the device sensitivity and reduced the optimum operating temperature

A room temperature polyaniline nanofiber hydrogen gas sensor

Abstract—Electro-conductive polyaniline (PANI) nanofiber based Surface Acoustic Wave (SAW) gas sensors have been investigated with hydrogen (H2) gas. A template-free, rapidly mixed method was employed to synthesize polyaniline nanofibers using chemical oxidative polymerization of aniline. The nanofibers were deposited onto a layered ZnO/64º YX LiNbO3 SAW transducer for gas sensing applications. The novel sensor was exposed to various concentrations of H2 gas at room temperature. The sensor response, defined as the relative variation in operating frequency of oscillation due to the introduction of the gas, was 3.04 kHz towards a 1 % H2 concentration. A relatively fast response time of 8 sec and a recovery time of 60 sec with good repeatability were observed at room temperature. Due to room temperature operation, the novel gas sensor is promising for environmental and industrial applications. I