After the 9∙11 terrorism and America-Iraq war, apprehension of mass destruction weapons such as bio-chemical agents calls for much more sensitive sensors which can detect toxic gases. In this study, semiconductor gas sensors based on tin oxide were examined to detect chemical agent simulants: dimethyl-methyl-phosponate (DMMP), di(propylene glycol) methyl ether (DPGME), acetonitrile, and dichloromethane. DMMP((CH3O)3), DPGME(C7H16O3), acetonitrile(CH3CN), and dichloromethane(CH2Cl2) gases are the simulants of nerve agent-sarin, vesicant agent-HN(N(CH2CH2Cl)3), blood agent-AC(HCN), and choking agent-CG(COCl2) gases, repectively. The SnO2 powder was prepared by a coprecipitation method from the mixture of tin chloride and zinc acetate dihydrate. Zinc oxide was doped into SnO2 from 1 wt% to 4 wt% to improve its reliability and sensitivity. To fabricate a thick film, powders were made into paste with organic binder of ethyl cellulose and screen-printed on the alumina substrate. The phase development and morphology of ZnO-doped SnO2 film were investigated by XRD (X-ray diffraction analysis), BET (surface and pore size analyzer), and SEM (scanning electron microscope). The gas sensing characteristics for target gases were examined with a flow-type measurement system. The concentrations of simulants were controlled from 500 ppb to 1500 ppb, and working temperatures were regulated from 250 to 400 .

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Nitrogen oxides (NO x ) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NOx emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO 2 sensors for CO and NO x were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO2 sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NOx gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO 2 sensors.

Indium tin oxide (ITO) films are widely used in optical devices for their high electrical conductivity and high transparency to visible light. Some relevant papers reported ITO thin films showed favorable sensitivity to NO 2 and NO gases. However, researches on gas sensing with ITO films, especially thick films, had not been actively conducted until now. The crystal structure and particle size of ITO can be controlled in nanometer accuracy by coprecipitation method. To investigate the effects of crystal structure and particle size of nanosized ITO powder on gas sensing properties, two kinds of ITO sensors, having cubic and rhombohedral crystal structures with 15 nm particle sizes, were investigated, and three kinds of ITO sensors having 15, 30, and 70 nm particle sizes, with the rhombohedral crystal structure, were investigated. Gas sensing properties were examined in a chamber with dry air (less than 1 ppm humidity concentration) or gaseous ethanol diluted in dry air. ITO gas sensors with the finer the particle sieze have better sensitivity than of large particle size. The sensitivity of ITO thick films were evaluated by sensing of gaseous ethanol.[ Received October 16, 2003; Accepted March 23, 2004] Keywords : ITO, Sensor, Coprecipitation method 1. Introduction Tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) is not widely used as a gas sensor material even though it shows high sensitivity and good longterm stability to NO and NO 2 . 1),2) Nonetheless, Indium oxide and tin oxide, respectively, are widely employed as the bases for solidstate gas sensors detecting combustible and toxic gases.3)5) To be a high sensitivity gas sensor, ITO thick film should be made of ultrafine powders(or ITO particles). Gas sensitivity is depen dent on the gas adsorption behavior, the particle size of the oxide, the microstructure of the sensing layer such as its porosity and neck size between two particles, and the catalytic activity of the metals (or metal oxides).Therefore, in this study, the effects of crystal structure and particle size on the gas sensing properties of ITO thick film were investigated. Among the powder processing techniques, coprecipitation technique has been suggested as a simple and economic way to obtain nanocrystalline ITO powders with good controlled particle size and morphology. 5)7) In the coprecipitation method, the morphology, particle size and composition of precipitates depend on several parameters such as aging time and temperature, pH and the kinds of anions present.7) Nanocrystalline ITO powders could be prepared us ing a coprecipitation method and the structures of the precipitates were controlled by varying the pH of solution dur ing the coprecipitation reaction and the aging time after coprecipitation. As a result, after calcining the precipitate, cu bic and rhombohedral nanocrystalline ITO powders were selectively produced. In 2 O 3 has polymorphisms that are both cubic and rhombohedral in structure. Cubic In 2 O 3 is a Ctype rare earth structure and has 16 molecules pe...