Materials for solid-state gas sensors (original) (raw)

Effect of particle size and dopant on properties of SnO 2-based gas sensors

Sensors and Actuators B-chemical, 2000

The effect of composition, microstructure, and defect chemistry on sensing performance of gas sensors based on CuO-doped SnO is 2 Ž . investigated using sol-gel derived nano-sized powders about 20 nm . The particle size of copper oxide doped tin oxide is varied by annealing at different temperatures and a significant grain growth is observed at temperatures above 10008C due to the liquid phase sintering effect of copper oxide. The reduction of particle size to nanometers, or to the dimension comparable to the thickness of charge depletion layer, leads to a dramatic improvement in sensitivity and speed of response. It appears that the substitution of Sn by Cu in the cassiterite structure increases the concentration of oxygen vacancies and decreases the concentration of free electrons. In particular, the Ž q . 2q existence of cuprous ions Cu , due to partial reduction of Cu during sintering, plays an important role in enhancing the sensor Ž . response to nitric oxide NO and CO . q

Synthesis and use of a novel SnO2 nanomaterial for gas sensing

Applied Surface Science, 2000

bstract w Ž . x Decomposition of the organometallic precursor Sn NMe in a controlled waterranisol mixture leads to the 2 2 2 formation of monodisperse nanocomposite particles of SnrSnO . Full oxidation of the particles into SnO occurs at 6008C x 2 without size or morphology change. These particles can be deposited onto silicon nitride covered microelectronic platforms and used as sensitive layers of gas sensors. Doping of the sensors with palladium can be achieved either by co-decomposi-Ž . tion of organometallic precursors doping in volume or by deposition of palladium on preformed SnO nanoparticles 2 Ž

Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview

2014

Ag-and Pd-loaded SnO 2 nanowire network sensors were prepared by the growth of SnO 2 nanowires via thermal evaporation, the coating of slurry containing SnO 2 nanowires, and dropping of a droplet containing Ag or Pd nanoparticles, and subsequent heat treatment. All the pristine, Pd-loaded and Ag-loaded SnO 2 nanowire networks showed the selective detection of C 2 H 5 OH with low cross-responses to CO, H 2 , C 3 H 8 , and NH 3 . However, the relative gas responses and gas selectivity depended closely on the catalyst loading. The loading of Pd enhanced the responses(R a /R g : R a : resistance in air, R g : resistance in gas) to CO and H 2 significantly, while it slightly deteriorated the response to C 2 H 5 OH. In contrast, a 3.1-fold enhancement was observed in the response to 100 ppm C 2 H 5 OH by loading of Ag onto SnO 2 nanowire networks. The role of Ag catalysts in the highly sensitive and selective detection of C 2 H 5 OH is discussed.

Applications of Nanostructured Materials as Gas Sensors

Gas detection instruments are increasingly needed for industrial health and safety, environmental monitoring, and process control. To meet this demand, considerable research into new sensors is underway, including efforts to enhance the performance of traditional devices, such as resistive metal oxide sensors, through nano-engineering. The resistance of semiconductors is affected by the gaseous ambient. The semiconducting metal oxides based gas sensors exploit this phenomenon. Physical chemistry of solid metal surfaces plays a dominant role in controlling the gas sensing characteristics. Metal oxide sensors have been utilized for several decades for low-cost detection of combustible and toxic gases. Recent advances in nanomaterials provide the opportunity to dramatically increase the response of these materials, as their performance is directly related to exposed surface volume. Proper control of grain size remains a key challenge for high sensor performance. Nanoparticles of SnO 2 have been synthesized through chemical route at 5, 25 and 50 o C. The synthesized particles were sintered at 400, 600 and 800 o C and their structural and morphological analysis was carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reaction temperature is found to be playing a critical role in controlling nanostructure sizes as well as agglomeration. It has been observed that particle synthesized at 5 and 50 o C are smaller and less agglomerated as compared to the particles prepared at 25 o C. The studies revealed that particle size and agglomeration increases with increase in sintering temperature. Thick films gas sensors were fabricated using synthesized tin dioxide powder and sensing response of all the sensors to ethanol vapors was investigated at different temperatures and concentrations. The investigations revealed that sensing response of SnO 2 nanoparticles is size dependent and smaller particles display higher sensitivity.

Synthesis, characterization and fabrication of gas sensor devices using ZnO and ZnO:In nanomaterials

Dopant elements solegel a b s t r a c t Undoped and In-doped ZnO including nanoparticles and nanorods were successfully synthesized via sol gel method. Effect of different doping ratios (1, 5 and 10%) of indium as a dopant element was optimized for the highest gas sensitivity. The morphological structures of prepared Undoped and doped ZnO were revealed using scanning electron microscope (SEM) and the aspect ratios of nanorods were calculated. X-ray diffraction (XRD) patterns reveal a highly crystallized wurtzite structure and used for identifying phase structure and chemical state of both ZnO and ZnO doped with In under different doping ratios. Energy dispersive X-ray (EDS) analysis was performed to be confirming the chemical composition of the In-doped ZnO nanopowders. The gas sensitivity for O 2 , CO 2 and H 2 gases were measured for the fabricated gas sensor devices as a function of temperature for In-doped ZnO nanopowders and compared with un-doped ZnO films.

P1. 0.13 Highly sensitive ZnO− SnO2 nanocomposite H2 gas sensor

Thin film sensors based on SnO 2 , ZnO and ZnO−SnO 2 nanocomposite have been fabricated using pulsed laser deposition technique. The prepared sensors were studied for their response characteristics towards 500 ppm H 2 gas. The nanocomposite sensor structure (ZnO−SnO 2 ) shows an enhanced response of about 8.8×10 2 as compared to that obtained (7 and 8) for bare ZnO and SnO 2 thin film sensors respectively at a relatively lower operating temperature of 160°C. The nanocomposite sensor shows an improvement in response and recovery speeds compared to that of pure ZnO film sensor, though the results are slightly degraded in comparison to the bare SnO 2 thin film based sensor structure. The origin of enhanced response of ZnO−SnO 2 composite sensor is attributed to the modulation of depletion region width at the n−n heterojunction besides the enhanced oxygen adsorption. The high sensing response obtained at low operating temperature for ZnO−SnO 2 composite sensor is attractive for efficient detection of H 2 gas.

Study of ZnO, SnO2 and Compounds ZTO Structures Synthesized for Gas-Detection

Engineering and Technology Journal, 2015

Semiconductor-based metal oxide gas detector of five mixed from chloride salts Z:S ratio (0,25,50,75,100%) were fabricated on Si (n-type) substrate by a spray pyrolysis technique with thickness were about ( 0.2 ±0.05 μm) using water soluble as precursors at a substrate temperature 500 Co±5, 0.05 M ,and their gas sensing properties toward (CO2 , NO2 and SO2 gas at different concentration (10,100,1000 ppm) in air were investigated at room temperature which related with the petroleum industry. Furthermore structural and morphology properties was scrutinize. Results shows that the mixing ratio affect the composition of formative oxides were (ZnO,Zn2SnO4,Zn2SnO4+ZnSnO3,ZnSnO3, SnO2) ratios mentioned in the above respectively, and related with the sensitivity of the tested oxidation gases. Key Word: Zinc stannate, gas sensor, ternary metal oxides, spray pyrolyess, pollutant gases, XRD.

New approaches for improving semiconductor gas sensors

Sensors and Actuators B: Chemical, 1991

It is demonstrated that the sensing characteristics of a semiconductor gas sensor using SnO, can be improved by controlling fundamental factors which affect its receptor and transducer functions. The transducer function is deeply related with the microstructure of the elements, i.e., the grain size of SnO, (D) and the depth of the surface space-charge layer (15). The sensitivity is drastically promoted when D is made comparable to or less than 2L, either by control of D for pure SnO, elements or by control of the Debye length for impurity-doped elements. On the other hand, the receptor function is drastically modified by the introduction of foreign receptors on the surface of SnO,. In the particular cases of Pd and Ag promoters, the oxides (PdO and Ag,O) formed in air interact with the SnO, surface to produce an electron-deficient space-charge layer, and this contributes much to promoting the gas sensitivity. For a test gas having a specific reactivity, such specificity can be utilized for exploiting gas-selective receptors, as exemplified by CuO-SnO, and La,O,-SnO, elements, which detect H,S and ethanol gas respectively very sensitively.

Solid‐State Gas Sensors: A Review

Journal of The Electrochemical Society, 1992

During the past three decades, gas sensors based either on the surface characteristics or the bulk electrolytic properties of ceramics, have been the subject of extensive research and development. The application of these sensors range from air-to-fuel ratio control in combustion processes such as in automotive engines and industrial furnaces to the detection of leakage of inflammable and toxic gases in domestic and industrial environments. While the solid-state physical sensors, measuring pressure, temperature, and other physical parameters have been commercially successful, less success has been achieved by their chemical analogs, to measure moderate to very low concentrations of gases of importance. These gases include: 02, H2, CO, CO2, NOx, SO=, propane, methane, ethanol, and so on. The semiconductor-based chemical sensors owe their popularity to their small size, simple operation, high sensitivity, and relatively simple associated electronics. However, most of them still suffer from nonselectivity. They also have poor shelf-life and are relatively less stable at higher temperatures. The sensing characteristics and performance of some of the solid-state gas sensors are reviewed in this paper, together with their sensing mechanism, which still is a gray area and has not been fully understood.