Advanced Materials Letters

We report investigations on resistive material SnO2: Cu (9 wt. %) evaluated and optimized for the application of gas sensor. SnO2: Cu has been thoroughly characterized by using X-ray photoelectron spectroscopy (XPS). The deconvolution of XPS spectra confirms the existing surface reactive species in the form of states of the metal orbital and the presence of multiple pathways for the detection of CO vis-à-vis sintering temperature effect. Enhanced CO pickup at the sintering temperature of   650 0 C (wide range and low sensitivity) and 750 0 C (short range and high sensitivity) has been observed. The CO sensing and XPS data correlates well along with the nonconventional use of variation in average XPS background intensity of general scan seems to be related to optimized sensitivity conditions of various gases. 

Nanocrystalline SnO2 oxides particles have been successfully synthesized via polyol process using diethylene glycol (DEG) as a solvent, followed by powder thermal treatment. The general applicability of the process is shown and the advantages in terms of properties and processability are described. The powders thus prepared were investigated using X-ray diffractometry. (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectra (PL). The X-ray diffraction patterns of the samples were indexed to the rutile phase for SnO2.The TEM images show uniform isotropic morphologies with average sizes close to10 nm. This decrease in particle size is accompanied with a decrease in the band-gap value from 3.55 eV for SnO2 down to 3.27 eV as shown by UV-visible spectra. It is demonstrated that the crystallite size less than 10 nm can be controlled by changing the quantity of added water (rate hydrolysis h=n H2O/n Metal).

Three dimensional (3D) complex microcrystal chains of SnO2 have been fabricated by simple carbothermal reduction based vapour deposition method. The structural and optical properties of the as-synthesized materials were well characterized by field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), Raman spectroscopy and photoluminescence spectroscopy. FESEM studies revealed the formation of 3D complex chains of microcrystals of SnO2 of varying shape and size. The SnO2 microcrystals have been found to be inter-connected through oriented attachment, leading to the formation of 3D complex chains of microcrystals. XRD studies showed the presence of SnO2 and Sn in the synthesized material. Photoluminescence studies on SnO2 microcrystal chains revealed peaks at 361, 407, 438 and 465 nm. A tentative mechanism of formation of the 3D complex chains of SnO2 microcrystals is proposed. These SnO2 microcrystal chains have potential applications as building blocks in novel functional devices.

The effect of Cu, Al and In doping on the microstructural and the electrical properties of the SnO2 films were studied. The undoped, Cu, Al and In (2 at. %) doped SnO2 films were deposited on the glass substrate by spray pyrolysis from 0.8 M SnCl2–ethanol solution at substrate temperature 400 °C. The microstructural properties of films were investigated by X-ray diffraction (XRD) method. It was determined that the films formed at polycrystalline structure in tetragonal phase and structure was not changed by dopant species. The lattice parameters (a), (c) and crystallite size (D) were determined and obtained in the range of 4.90-4.92 Å, 3.26-3.31 Å and 34-167 Å, respectively. The optical transmittance of thin films was measured and the optical band gap Eg values of the films were obtained in the range of 3.96-4.00 eV, using the Tauc relation. The electrical transport properties of undoped, Cu, Al and In-doped SnO2 films were investigated by means of conductivity measurements in a temperature range of 120-400 K. The electrical transport mechanism of the undoped, Cu, Al and In-doped SnO2 films was determined by means of the tunneling model through the back-to-back Schottky barrier and the thermionic field emission model in the temperature range of 120-300 K and 300-400 K, respectively.

In the present work an effort has been made to synthesize nanocrystalline composites (NCC) of Zinc oxide and Tin oxide (ZSO) using chemical route for efficient sensing of NO2 gas at lower operating temperature. The structural, microstructural and optical information have been revealed by X-ray diffraction (XRD), Atomic force microscopy (AFM) and UV-Visible spectroscopy respectively. Sensor structure showed a better sensing response (S ~ 6.64×10 2 ) at a relatively low operating temperature of 70 °C for 20 ppm NO2 gas with an average response time of about 2 min. The sensing response characteristics for NO2 gas has been compared with corresponding results obtained for pure SnO2 and ZnO thin film based sensor structure.

Synthesized nanophase SnO2 powder is used to fabricate thick film resistors using screen printing technology. The surfaces of the thick film resistors were modified by dip coating in platinum chloride (PtCl2) solution of optimized 1.5 M for different time periods of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 minutes. Sintering of the films is carried out at different temperatures of 550, 600, 650, 700, 750 and 800°C. The films were tested for 400 ppm of LPG. Thick films which were dip coated for 5 minutes and sintered at 750 o C show the highest sensitivity towards LPG which is ten times higher than undoped SnO2 sensors. The characterization of the sensors was done using XRD, EDX and SEM. The sensors were found to be extremely stable and repeatable with a response and recovery time of 10 and 22 s with a minimum detection limit of 5 ppm of LPG.

One-dimensional wire shaped tin oxide (SnO2) nanostructures have been synthesized by thermal evaporation method. The growth of SnO2 nanostructure was carried out on gold catalyst layer coated silicon substrate. X-ray diffraction (XRD) results reveals that synthesized SnO2 nanowires have polycrystalline nature with tetragonal rutile structure. SEM, TEM and EDX observation concludes that the uniform SnO2 nanowires (diameter ~ 40 nm and length ~ 50 μm) grow with vapor-liquid-solid (VLS) mechanism. I-V characteristics of single SnO2 nanowire show semiconducting behaviour. Due to structural and electrical properties of SnO2 nanowire, these nanowires would be a promising candidate for gas sensing applications.