Gas Sensing Properties Of SnO Research Articles

Effect of Substrate Temperature on Porosity and Gas Sensing Properties of SnO2-B: Doped Polypyrrole Thin Films

Porous SnO2-B: doped polypyrrole thin films were synthesized by the dissolving 0.15M of stannous chloride (SnCl4.5H2O) (10%, 20%, 30%, 40%, and 50%) in 25ml of ethanol and adding 4% of Boric acid (H3BO3) and polypyrrole (1:1) using chemical spray pyrolysis technique. Studies on effect of substrate temperature on porosity of the deposited films were at four different temperatures ranging 200⁰C to 280⁰C. The H2S gas was used to study the gas sensing behavior of deposited films and all films were characterized by using IR, XRD, SEM, UV-Vis spectrometry, and current-voltage measurement.

Effects of Oxygen and Carbon Monoxide Species on the Gas Sensing Properties of SnO2 Nanoparticles

Effects of Oxygen and Carbon Monoxide Species on the Gas Sensing Properties of SnO₂ Nanoparticles

Synthesis and Gas Sensing Properties of SnO<sub>2</sub> Nanostructures by Thermal Evaporation

Tin oxide nanostructures (NS) were grown on silicon substrates by thermal evaporation method with three different parameters. These parameters were temperatures (650 °C, 750 °C and 850 °C), nickel catalyst concentrations (0, 5 and 10 milimoles) and tin powder source to substrate distances (2 cm, 4 cm and 6 cm). The parameters were found to affect the size and morphology of the synthesized nanostructures. Formation of nanospheres (NSs), nanoneedles (NNs) and nanowires (NWs) of tin oxide were observed by Scanning Electron Microscope (SEM) at different synthesis conditions. Synthesis temperature was found to have most pronounced effect on the size and morphology of the nanostructures. Catalyst concentration has affected the porosity and growth of the nanostructures. The distance between source and substrate affected the nanostructures predominately on distribution and particle size. Energy dispersion X-ray (EDX) analysis confirms the presence of tin and oxygen in all nanostructures at all synthesis conditions. X-ray diffraction (XRD) proves the formation of tin oxide phase in all samples. Significant formation of tin oxide nanowires was observed at 850 °C. Gas sensing properties of SnO2 nanowires (NW) toward ethanol (C2H5OH) gas at 450°C with different volume concentration was measured. It was found SnO2 NW had good sensing properties for C2H5OH at 100 ppm compared to measurements made at 25-50 ppm.

Alkaline- and template-free hydrothermal synthesis of stable SnO 2 nanoparticles and nanorods for CO and ethanol gas sensing

SnO 2 nanoparticles and nanorods are synthesized via a facile template-free hydrothermal method, using SnCl 2·2H 2O and deionized water without any alkaline solution. The influences of the hydrothermal reaction time in the range of 5–48 h and temperatures of 130 and 160 °C and also calcination temperature on the size and morphological and gas-sensing properties of SnO 2 particles were investigated. The SnO 2 samples were characterized by X-ray diffraction analysis (XRD), surface area analyzer (using BET method) and scanning electron microscopy. The response of the SnO 2 nanostructures sensors to ethanol and various concentrations of CO were measured in an automated flow setup at different temperatures. As the hydrothermal synthesis temperature and time increases, the crystallite sizes enlarge nonlinearly and morphology of SnO 2 nanostructures changes from nanoparticles to nanorods. The most SnO 2 samples are thermally stable at calcination temperature of 350 °C. SnO 2 nanoparticles as small as 3.1 nm with the highest specific surface area of 254 m 2/g are hydrothermally synthesized at 130 °C in 5 h. This sample shows the highest response of 30 and 2565 to 1000 ppm CO and ethanol at 200 and 250 °C, respectively.

Synthesis and gas-sensing properties of nano- and meso-porous MoO 3-doped SnO 2

Nano- and meso-porous SnO 2 powders doped with and without 1–10 wt% MoO 3 have been synthesized by an ultrasonic spray-pyrolysis method employing a precursor aqueous solution containing tin (IV) chloride pentahydrate (SnCl 4·5H 2O), ammonium heptamolybdate and polymethylmethacrylate (PMMA) microspheres as a template, and the effects of MoO 3-doping and the addition of PMMA microspheres on the structural, morphological and gas-sensing properties of SnO 2 were investigated in this study. It is confirmed that control of the amounts of PMMA microspheres in the precursor solution was effective in realizing well-developed nano- and meso-porous structures of SnO 2 by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and the measurement of specific surface area and pore size distribution using a N 2 adsorption isotherm. Gas-sensing properties of their thick films (about 50 μm thick), which were fabricated by screen-printing to various gases (NO 2, C 2H 5OH and H 2) were tested in ambient air. The doped thick films showed a high response and selectivity to 5 ppm NO 2 gas in the case of 10 wt% MoO 3-doping in both nano- and meso-porous structures of SnO 2. We observed that the presence of Mo species in SnO 2 lattice can improve the sensor response and selectivity towards NO 2 gas. The effect of the MoO 3-doping on the sensing characteristics of these films towards NO 2 was discussed.

Gas-sensing properties of SnO 2–TiO 2-based sensor for volatile organic compound gas and its sensing mechanism

We report the microstructure and gas-sensing properties of the SnO 2–TiO 2 composite oxide dope with Ag ion prepared by the sol–gel method. Of all various volatile organic compounds (VOCs) such as ethanol, methanol, acetone and formaldehyde were examined, the sensor exhibits remarkable selectivity to each VOCs at different operating temperature. Further investigations based on quantum chemistry calculation show that difference orbital energy of VOCs molecule may be a qualitative factor to affect the selectivity of the sensor.

Direct fabrication of SnO 2-based thick film gas sensor using Micropen direct writing and laser microcladding

A direct-write technique for rapid prototyping and manufacturing of SnO 2 thick film gas sensor has been presented in this paper. The technique combined Micropen direct writing, which deposited electronic pastes onto substrate according to the designed pattern, with laser microcladding to produce finer electrical components to overcome the resolution limitation of Micropen direct writing. With computer-aided design/computer-aided manufacturing (CAD/CAM), gas sensors with complicated patterns have been fabricated successfully by this technique without any mask. Nano-scale SnO 2 paste without any doping element was used and irradiated by a continuous-wave laser with varied power. The effect of laser power on microstructure and gas-sensing properties of SnO 2 thick film gas sensors has been investigated. The results indicate that the gas sensor fabricated by this hybrid technique exhibits excellent gas-sensing properties quite similar to those of screen-printed sensors.

Gas-sensing properties of ordered mesoporous SnO 2 and effects of coatings thereof

Mesoporous structure and gas-sensing properties of SnO 2 powders prepared by utilizing the self-assembly of a cationic surfactant under different conditions have been investigated. As-prepared SnO 2 powders were characterized with ordered and hexagonal mesoporous structure ( d 1 0 0 ≈4.4 nm) having a small crystallite size of 1.6–2.0 nm, and the size of agglomerated secondary particles tended to decrease with decreasing the concentration of a Sn source and a surfactant in a precursor solution. Treatment of as-prepared powders with phosphoric acid (PA) was effective for depressing the growth of SnO 2 crystallite during calcination at elevated temperatures and then maintaining the ordered mesoporous structure, while the volume of ordered mesopores decreased. However, mesoporous SnO 2 (m-SnO 2) powder with a specific surface area of 374 m 2 g −1 could be prepared even after calcination at 600 °C for 5 h by optimizing the preparation conditions. The m-SnO 2 powders exhibited excellent H 2 sensitivity in proportion to surface area and high NO sensitivity comparable to NO 2 sensitivity. However, their resistance levels in air were close to the limit for practical measurement. Surface modification of conventional SnO 2 (c-SnO 2) powder with m-SnO 2 was found to be effective for improving gas-sensing properties of c-SnO 2, while maintaining the sensor resistance in air to be close to that of c-SnO 2. H 2 sensitivity of the c-SnO 2 modified with m-SnO 2 was lower than that of m-SnO 2, but NO 2 sensitivity improved markedly by the surface modification with m-SnO 2.

Influence of the Particle Size on the Surface Reactivity and Gas Sensing Properties of SnO<SUB>2</SUB> Nanopowders

The surface reactivity of a powder depends on the chemical composition of its surface and on the presence of defects. In the case of nanosized powders, the surface reactivity is enhanced by the increased defect concentration on the surface. On the other hand, the gas sensing properties of a semiconductor material are strongly related to the surface reactivity. In this article, it is shown, by Fourier transform infrared spectrometry, that SnO2 semiconductor nanoparticles are very sensitive toward CO and that the decrease of the particle size greatly enhances this sensitivity. Comparison is made between particles having an average size of 15 and 8 nm. Surface reactions at the origin of the CO detection mechanism are discussed as a function of the particle size.

Hydrogen sensing properties of SnO 2 subjected to surface chemical modification with ethoxysilanes

Effects of surface chemical modification with triethoxymethylsilane (TEMS) and ethoxy-trimethylsilane (ETMS) on the gas-sensing properties of SnO 2 have been investigated, in comparison with the modification with diethoxydimethylsilane (DEMS) in our previous report. The largest amount of SiO 2 was incorporated on the SnO 2 surface with the modification with TEMS, which had three ethoxyl groups in a molecule. The temperature-programmed desorption (TPD) peaks of O − or O 2− adsorbates and surface hydroxyl groups decreased to disappear with the repeated modification. These observations confirm that chemical fixation of the SiO 2 component on the SnO 2 proceeds via dehydration–condensation reaction between the ethoxyl and hydroxyl groups on the SnO 2 surface. Electrical resistance in air of the SnO 2 sensors increased straightly with the amount of the incorporated SiO 2, suggesting that the Schottky potential barrier heights at the grain boundaries increased due to the suppressed neck growth between SnO 2 grains. A significant increase in sensitivity to H 2 was also observed with the repeated incorporation of SiO 2 on the SnO 2 surface, irrespective of the kind of ethoxysilane, though the sensitivity decreased at a larger amount of SiO 2 in the case of TEMS-modification. On the other hand, sensitivity to C 3H 8 and CH 4 showed a maximum at a certain amount of the incorporated SiO 2 (Si/Sn≈0.004), and decreased at the larger amounts, again irrespective of the kind of ethoxysilane. The sensitivity enhancement at the small amount of SiO 2 was thought to be ascribable to the increased potential barrier heights at the grain boundaries, while the decrease at the larger amounts corresponded to the decreased catalytic activity for C 3H 8 and CH 4 oxidation.

Effects of Pd- and Pt-loading on the Gas-sensing Properties of SnO<sub>2</sub> Subjected to Surface Chemical Modification with Diethoxydimethylsilane

Effects of Pd- and Pt-loading on the Gas-sensing Properties of SnO<sub>2</sub> Subjected to Surface Chemical Modification with Diethoxydimethylsilane

Preparation, development of microstructure, electrical and gas-sensitive properties of pure and doped SnO 2 powders

The influence of bulk dopants (Nb, Mn, In and Pd) on the morphological, electrical and gas-sensing properties of SnO 2 powders was observed. Comparing the specific surface areas of the powders observed by BET Nb-doping results in very fine powders. The electrical resistivity of SnO 2 is decreased by Nb-doping and increased by bulk doping with either Pd, Mn or In. The existence of solid solutions in the systems doped with Nb, Mn and In is confirmed by single crystal experiments. The gas sensitivities are strongly correlated with the electrical resistivities of the sensor elements. The complex influence of dopants on the morphological and electrical properties of SnO 2 is demonstrated by establishing a relation between the crystallite diameter, an evaluated carrier concentration, the number of electrons per crystallite and the thickness of the electron depletion layer. A limitation of bulk doping with electron-compensating elements for sensor optimization is given.

Gas-sensing properties of SnO 2 pyrolytic films subjected to ultrviolet radiation

Chemisorption of different species changes the electrical resistivity of many semiconductor films. In this work we have studied the behavior of thermally treated SnO 2 films. At room temperature thermal desorption of many species is negligible in this material, so the electrical resistivity of the SnO 2 films remains invariant with various gas compositions in the surrounding. To operate a gas sensor at room temperature with this material, we have used UV-radiation to produce photodesorption. At the same time this radiation produces photodissociation of the chemisorbed molecules. Using nitrogen as a carrier gas, small amounts of acetone and trichloroethylene vapors are injected into the system, measuring the current through the films with a constant applied voltage. Selectivity is achieved in this case by using filters that modify the IV excitation spectrum. The short-wavelength cut-off of this spectrum should be no longer than about 3200 Å, corresponding to the minimum photon energy to excit electron-hole pairs in the SnO 2 films. Nitrogen/oxygen gas transitions have been investigated.