Effects of surface silver additives on tin oxide thin film gas sensors (original) (raw)
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Field-assisted diffusion of silver in SnO2 thin films
Journal of Physics: Conference Series
Tin oxide films are known for their wide spread applications in the field of optoelectronics as transparent conductors and as atmosphere sensitive ceramic pellets for chemical sensor fabrication. Forming durable ohmic contacts to these films is vitally necessary for the effective performance and long life of almost all such devices. Silver electrodes are commonly considered as low resistance ohmic contacts to many metal-oxide semiconductors. Particularly in devices operating at elevated temperatures, silver migration can considerably decrease useful device lifetime. Here, we study the performance of silver electrodes paste printed on SnO2 thin films and show that the I-V characteristics of the silver/SnO2 contact changes with operating time at elevated temperatures. SnO2 films are grown on alumina substrates by ultrasonic spray pyrolysis technique. A pair of Ag electrodes are paste-printed on the surface of the grown films followed by a heat-treatment step to stabilize the deposits. The as-fabricated Ag/SnO2 contacts present ohmic characteristics. Continuous application of DC voltages to the samples operating at 350 °C results in a significant drop in the devices' resistance. The results originate from field-assisted migration of silver ions from the anode to the cathode electrode and formation of Ag micro-filaments in the polycrystalline SnO2 layer.
A model for the gas sensing properties of tin oxide thin films with surface catalysts
Sensors and Actuators B-chemical, 1995
The effect of two types of surface additives (Pd and Pt) on the response of reactively sputtered thin films of SnO. gas sensors has been studied, in mixtures of zero grade air and carbon monoxide. The experimental results obtained with surface additives show an abrupt conductance increase around 500 K when carbon monoxide in the ppm range is present, a behaviour which has not been observed with plain SnO, films. A semi-empirical model that explains this behaviour is presented, that is based on the well-established theory for the conductivity of ultrathin discontinuous metal films, i.e. activated charge carrier creation and tunnelling through potential barriers. The proposed model takes into account the dependence of film conductivity both on the thickness of the noble metal deposited on it and on the working temperature. The results of the theoretical analysis are in excellent qualitative agreement with the experimental ones.
Interaction of reducing gases with tin oxide films prepared by reactive evaporation techniques
SnO 2Àx films were prepared by reactive thermal and e-beam evaporation of Sn on alumina substrates and by post deposition thermal treatment. X-ray diffraction measurements found that films are tin dioxide (SnO 2 ) phase with small amounts of SnO phase. The surface conductivity of films was measured in air and in presence of H 2 S, H 2 and C 2 H 5 OH vapors at four sensor operating temperatures of 433e493 K. The resistance of SnO 2Àx films decreases on exposure to H 2 S but shows no change with hydrogen and ethanol. H 2 S response decreases with rise in sensor temperature while both response and recovery times improve. H 2 S signal enhances with increase in resistivity of SnO 2Àx coatings. Our experiments conclude that increase in film conductance is due to chemical reaction between H 2 S and SnO 2Àx surface and there is little or no role of interaction of gas molecules with surface adsorbed charged oxygen species.
Synthesis of Ag doped SnO2 thin films for the evaluation of H2S gas sensing properties
Physica B: Condensed Matter, 2017
The Tin Oxide (SnO 2) based thin films doped with 1.5, 3.0 and 4.5 mol% of Ag were deposited on the glass substrates using the advanced chemical spray pyrolysis technique. All the films were deposited at temperature 400°C. The crystalline structure of the samples was analyzed by X-ray diffraction (XRD). All the XRD patterns of the films showed a well-defined polycrystalline phase, fitting well with the SnO 2 tetragonal rutile type structure. The optical properties of the Ag doped SnO 2 films were studied using UV-Visible absorption spectroscopy. The surface morphological analysis of as-synthesized Ag doped SnO 2 films have been carried out using scanning electron microscope (SEM). The sensor response was estimated by the change in the electrical resistance of the film in the absence and presence of H 2 S gas. The sensor response and sensitivity in relation to, operation temperature and the gas concentration have been systematically studied. A significant response (∼ 1.38) and with a short response and recovery time (46 s, 110 s) towards 450 ppm H 2 S at 100°C operating temperature is observed for the 3 mol% Ag-doped SnO 2 film. This method offers a highly promising candidate for development of materials sensors due to facile fabrication route and desirable sensing performance.
Effect of silver additive on electrical conductivity and methane sensitivity of SnO2
Materials Science in Semiconductor Processing, 2015
A composite powder of tin oxide (SnO 2 ) and silver (Ag) clusters was prepared by a simple and cost effective method of reducing their aqueous mixture with sodium borohydride (NaBH 4 ). Gas sensors based on the composite were made by powder pressing procedure and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrical conductivity and gas sensing behavior of the sensors for methane (CH 4 ) gas were studied as a function of Ag concentration (0.3, 0.5, 0.8 and 1.5 wt%). The Ag additive is found to improve sensor response and widen its working temperature range with notable sensor response. The best sensor response was achieved by the sensor with 0.5 wt% Ag. The enhanced response was proved to be due to both electrical and chemical mechanisms.
Materials Characterization, 2007
The gas-sensitivity properties of SnO 2 thin films as well as Ag/SnO 2 and SnO 2 /Ag structures in an atmosphere containing propane (C 3 H 8 ) were examined. The SnO 2 and Ag films were deposited by a spray pyrolysis technique and vacuum evaporation, respectively. Soda-lime glass was used as the substrate for all the structures in this study. The sensors were measured in a propane atmosphere with different gas concentrations (50, 100, 200, 300, 400, and 500 ppm) at different operation temperatures (22, 100, 200, and 300°C). The Ag/SnO 2 structure, sintered a 400°C for 1 h, showed the highest sensitivity, of the order of 400 at an operation temperature of 200°C. The results show that the addition of Ag in the tin oxide films effectively acts as a catalyst in propane sensors and confirm the potential feasibility of using Ag as a catalyst in SnO 2 -based propane sensors.
Journal of Nepal Physical Society, 2021
In this article SnO2 thin films have been deposited onto glass substrates by Spray Pyrolysis Method. Tin chloride dihydrate (SnCl2.2H2O) and Copper nitrate (Cu (NO3)2 .3H2O) were used as source of Sn and Cu respectively. The structural, optical and gas sensing properties of Undoped and copper doped by (vol. %) SnO2 film have been investigated. XRD of film shows structure of films. Also result so obtained from XRD spectroscopy shows that these layers have the tetragonal polycrystalline tinoxide structure. The optical transmission was found to decrease with addition of copper as dopant on SnO2 with the addition of Cu except for 5% Cu-Doped. The reponse of these layers have been investigated for different concentrations of butane gas by static gas sensing system. The results of this investigation show that the Cu-Doped SnO2 nanostructure layer compared with the pure SnO2 nanostructure layer has showed the better response for butane gas. Among Cu-Doped SnO2 thin film layer 4% (by vol.) ...
Effect of MgO and V2O5 Catalyst on the Sensing Behaviour of Tin Oxide Thin Film for SO2 Gas
Conference Papers in Science, 2014
The present work shows the SO2 gas sensing property of SnO2 thin film based sensor prepared by using RF sputtering technique. Different catalysts (MgO and V2O5) in form of nanoclusters having diameter of 600 μm have been loaded on SnO2 surface to detect SO2 gas. The sensing response of all these films towards SO2 is monitored. Microstructural studies have been carried out using XRD and UV-Visible Spectrophotometer and a good correlation has been found between the microstructural and gas sensing properties of these deposited samples. Both catalysts when incorporated with SnO2 film show high selectivity towards SO2 gas at lower operating temperature. MgO gives a sensitivity of 317% at an operating temperature of 280°C towards 500 ppm of SO2 gas whereas V2O5 catalyst gives a sensitivity of 166% at 280°C for the same amount of gas.
XPS, TDS, and AFM studies of surface chemistry and morphology of Ag-covered L-CVD SnO2 nanolayers
Nanoscale research letters, 2014
This is well known that the selectivity and sensitivity of tin dioxide (SnO2) thin film sensors for the detection of low concentration of volatile sulfides such as H2S in air can be improved by small amount of Ag additives. In this paper we present the results of comparative X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and atomic force microscopy (AFM) studies of the surface chemistry and morphology of SnO2 nanolayers obtained by laser-enhanced chemical vapor deposition (L-CVD) additionally covered with 1 monolayer (ML) of Ag. For as deposited SnO2 nanolayers, a mixture of tin oxide (SnO) and tin dioxide (SnO2) with the [C]/[Sn] ratio of approximately 1.3 was observed. After dry air exposure, the [O]/[Sn] ratio slightly increased to approximately 1.55. Moreover, an evident increasing of C contamination was observed with [C]/[Sn] ratio of approximately 3.5. After TDS experiment, the [O]/[Sn] ratio goes back to 1.3, whereas C contamination evidently d...