P.P. Sahay

Influence of Cu doping on the structural, photoluminescence and formaldehyde sensing properties of SnO2 nanoparticles

In this paper we report Cu doping induced modifications in the structural, photoluminescence and gas sensing behaviour of SnO2 nanoparticles. Our results show that crystallinity is reduced upon Cu doping. The PL emissions observed in the visible region are attributed to the defect levels arising due to oxygen vacancies. The 1.5 at% Cu-doped SnO2 shows the selective high response (∼80%) to 50 ppm concentration of formaldehyde over methanol, ethanol, propanol-2-ol, acetone and n-butylacetate at 200 °C. The sensing mechanism has been explained based on chemisorption of oxygen on the SnO2 surface and the subsequent reaction between the adsorbed oxygen species and the formaldehyde molecules.

Spray-deposited nanocrystalline WO3 thin films prepared using tungsten hexachloride dissolved in N-N dimethylformamide and influence of in doping on their structural, optical and electrical properties

Undoped and In-doped nanocrystalline tungsten oxide (WO3) thin films were prepared by chemical spray pyrolysis using tungsten hexachloride (WCl6) dissolved in N-N dimethylformamide as the host precursor solution and indium chloride (InCl3) as the source of dopant. XRD analyses confirm the monoclinic phase of the prepared films with the predominance of triplet (002), (020) and (200) in the spectra. On indium doping, the crystallinity of the films decreases and becomes minimum at 1.5 at. % doping. EDX analyses confirm the incorporation of In dopants into the WO3 lattice network. SEM micrographs show nonspherical grains over the surface and the average grain size decreases with higher In doping. AFM images of the films exhibit large nicely separated conical columnar grains (except in 1 at. %) throughout the surface with coalescence of some columnar grains at few places. UV-visible measurements reveal that the optical transmittance of the 1 at. % In-doped film increases significantly throughout the wavelength range 300–800 nm relative to that of the undoped film. Room temperature photoluminescence spectra show pronounced enhancement in the peak intensity of NBE emission on In doping. Electrical conductivity has been found to increase on In doping.

Nanocube In2O3@RGO heterostructure based gas sensor for acetone and formaldehyde detection

Here, we studied the gas sensing response properties for acetone and formaldehyde by a chemiresistive nanocube In2O3@RGO heterostructure sensor. The nanocube In2O3@RGO heterostructure based sensor demonstrates a high response to acetone (∼85%) and formaldehyde (∼88%) at 25 ppm concentration and optimum working temperatures of 175 °C and 225 °C, respectively. Additionally, we examined the influence of potential barrier heights in the response/recovery time of the nanocube In2O3@RGO heterostructure based acetone and formaldehyde gas sensor. The real-time response/recovery analysis reveal that the sensor response depends on the potential barrier height as well as adsorbed active sites (O2− & O−) on the sensor surface. Furthermore, the nanocube In2O3@RGO heterostructure based gas sensor shows good selectivity to acetone and formaldehyde at optimum working temperature of 175 °C and 225 °C, respectively, compared to the other interfering gases such as ethanol, methanol, chloroform, toluene, benzene, ammonia, formic acid and acetic acid. The life-time analysis has been performed for 30 days, which showes the stability of nanocube In2O3@RGO heterostructure based acetone and formaldehyde sensor.

Tailoring the Microstructural, Optical, and Electrical Properties of Nanocrystalline WO3 Thin Films Using Al Doping

We have studied the influence of Al doping on the microstructural, optical, and electrical properties of spray-deposited WO3 thin films. XRD analyses confirm that all the films are of polycrystalline WO3 in nature, possessing monoclinic structure. EDX profiles of the Al-doped films show aluminum peaks implying incorporation of Al ions into WO3 lattice. On Al doping, the average crystallite size decreases due to increase in the density of nucleation centers at the time of film growth. The observed variation in the lattice parameter values on Al doping is attributed to the incorporation of Al ions into WO3 lattice. Enhancement in the direct optical band gap compared to the undoped film has been observed on Al doping due to decrease in the width of allowed energy states near the conduction band edge. The refractive indices of the films follow the Cauchy relation of normal dispersion. Electrical resistivity compared to the undoped film has been found to increase on Al doping.

Cr-induced modifications in the structural, photoluminescence and acetone-sensing behaviour of hydrothermally synthesised SnO2 nanoparticles

Cr-doped SnO2 nanoparticles have been synthesised by the hydrothermal route, using SnCl4·5H2O as the host precursor and C15H21CrO6 as the source of dopant. The structural and morphological studies have been carried out by X-ray diffraction, transmission electron microscopy and scanning electron spectroscopy, which reveal a tetragonal rutile structure of SnO2 nanoparticles and improvement in the crystallinity upon Cr doping. Compositional analyses by energy-dispersive X-ray confirm the incorporation of Cr ions into the SnO2 lattice. The existence of defect levels in the visible region has been studied by photoluminescence. The room-temperature electrical conductivity decreases with Cr doping due to the replacement of Sn4+ ions by Cr3+ ions. The response to acetone has been found to improve with the increase of Cr-doping concentration relative to the undoped SnO2, except in the case of 0.5 at% Cr-doped sample where it decreases at low concentrations (up to 30 ppm) and operating temperatures (up to 200 °C). The response time decreases with the increasing Cr-doping concentration and is found to be minimum for the 1.5 at% Cr-doped SnO2. A possible reaction mechanism of acetone sensing has been explained.