Narrow Results

Tin Oxide has been explored for gas sensing and humidity sensing. In the present work, pure and copper-doped SnO₂ is synthesized by controlled spray pyrolysis technique. The films are homogeneous throughout. Rietveld analysis confirms the absence of other phases due to doping. The optical property is studied using UV-Visible spectroscopy which shows a change in the band gap with the introduction of the dopant. An elaborate impedance analysis is carried which showed the effect of doping. Cu-doped thin film showed a faster drop in the impedance when exposed to humidity. Significant change in the cole–cole plot is observed indicating better sensitivity with the doped sample in comparison to undoped. Higher humidity level from 80 to 92 RH is studied as it is important to detect the same in air conditioning systems, electronic devices, aviation systems and food processing systems. The equivalent circuit also reveals that the adsorption of water molecules on the surface of the thin films changes the impedance characteristics. Levenberg–Marquardt algorithm is employed for the theoretical calculations and identifying the equivalent circuit. The charge transfer in the doped sample is subjected to lesser grain resistance according to theoretical calculation and experimental results. A density functional approach is employed to study the band structure and explain the influence of Cu doping on pure SnO₂. The calculated result supports the use of Cu as a dopant for better humidity sensing device.

In this paper, the humidity sensing properties of multi-walled carbon nanotubes modified with LiClO₄ was investigated. FTIR spectra showed that the ends of carbon nanotubes purified with nitric acid was opened and saturated with carboxylic acid groups and carboxylate groups. For comparison, the humidity sensing characteristics of four elements, MnWO₄ (Hubnerite), BaTiO₃ (Perovskite), NiWO₄ (Huberite), ZnCr₂O₄ (Spinel) were discussed. Experimental data showed that LiClO₄/MWNTs element exhibited excellent humidity sensing properties, that is, the response time can reach 7 min, the recovery time within 1 min and its sensitivity up to 35 000. Also, it was found that a small increase in resistance of pure MWNTs disappeared during the first few minutes after exposure to water by modifying with LiClO₄. The static and dynamic measurements showed that WMNTs/LiClO₄ sensing element exhibited high sensitivity and selectivity to water vapor.

Ultrafine Co₃O₄/SiO₂ nanocomposites were obtained via sol–gel (SG) method and related routes. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption–desorption techniques. The obtained phase, size of crystallites and specific surface area of the composites vary with the Co:SiO₂ weight ratio and preparation route. Humidity sensing properties measured by monitoring the DC conductivity for the obtained nanocomposites are reported. Conductivity changes amount to four orders of magnitudes were observed in response to 10–90% relative humidity change in the measuring chamber. Results indicate that humidity sensing properties depend on Co content and specific surface area of the composite.

Here, we report investigations on the relative humidity (RH) sensing property of ZnO nanotubes synthesized via hydrothermal method. Grown nanotubes are formed with a hexagonal shape and possess a wurtzite crystal structure in conjunction with higher oxygen vacancies. ZnO nanotube-based RH sensor shows a small current increase in lower RH (<75% RH) region, due to the frozen motion of H${}^{+}$ ions, where electronic conduction dominates. The sensor conduction increases from 13 to 960 fold upon exposer of 65%–90% RH, respectively. The free motion of H${}^{+}$ ions steers the conduction mechanism to be protonic in higher level physisorbed water layer and is responsible for the observed sharp increase in response. The competitive adsorption and desorption of oxygen species and water molecules play a vital role in defining the conduction to be electronic or protonic during the experiment.

This paper deals with the facile approach to the synthesis of different metal oxide nanoparticles and their comparative study for humidity sensing application at room temperature. The synthesis of these metal oxide nanoparticles is through co-precipitation method for nickel oxide and tin ferrite and hydrothermal route for cuprous oxide. The SEM and EDX reveal the porous morphology and confirmed composition of the synthesized metal oxides. FTIR detects the presence of functional groups like –OH and confirms the inverse spinal structure in tin ferrite. The optical band gap was determined by UV spectroscopy: 3.86eV for NiO, 4.13eV for Cu₂O, and 4.07eV for SnFe₂O₄. XRD gives the information about the average crystallite size for tin ferrite 2.42nm, cuprous oxide 12.88nm and nickel oxide 22.51nm as the size comes to nano range the surface area increases, which is a good indication for humidity sensing. The humidity sensing of materials was detected by electrical modes. The deposited thin films were prepared by spin coater and observed sensitivity of these films was 0.72M$\mathrm{\Omega }$/%RH for NiO, 1.59M$\mathrm{\Omega }$/%RH for Cu₂O, and 2.07M$\mathrm{\Omega }$/%RH for SnFe₂O₄. The experiments were repeated after few weeks and the aging effects of samples were found negligible which makes the sensor stable.