• Journal of Sensor Science and Technology
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• v.22 no.4
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• pp.302-307
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• 2013

The Sb-doped $SnO_2$ nanowire network sensors were prepared by thermal evaporation of the mixtures between tin and antimony powders. Pure $SnO_2$ nanowire networks showed high sensor resistance in air ($99M{\Omega}$), similar gas responses to 4 diffferent gases (5 ppm $C_2H_5OH$, CO, $H_2$, and trimethylamine), and very sluggish recovery speed (90% recovery time > 800 s). In contrast, 2 wt% Sb-doped $SnO_2$ showed the selective detection toward $C_2H_5OH$ and trimethylamine, relatively low resistance ($176k{\Omega}$) for facile measurement, and ultrafast recovery speed (90% recovery times: 6 - 18 s). The change of gas sensing charactersitics by Sb doping was discussed in relation to gas sensing mechanism.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.222-227
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• 2018

$Zn_{1-x}Co_x$ Zeolitic Imidazolate Framework (ZIF) (x = 0~0.05) were prepared by the co-precipitation of $Zn^{2+}$ and $Co^{2+}$ using 2-methylimidazole, which were converted into pure and Co-doped ZnO nanoparticles by heat treatment at $600^{\circ}C$ for 2 h. Homogeneous Zn/Co ZIFs were achieved at x < 0.05 owing to the strong coordination of the imidazole linker to $Zn^{2+}$ and $Co^{2+}$, facilitating atomic-scale doping of Co into ZnO via annealing. By contrast, heterogeneous Zn/Co ZIFs were formed at $x{\geq}0.05$, resulting in the formation of $Co_3O_4$ second phase. To investigate the potential as high-performance gas sensors, the gas sensing characteristics of pure and Co-doped ZnO nanoparticles were evaluated. The sensor using 3 at% Co-doped ZnO exhibited an unprecedentedly high response and selectivity to trimethylamine, whereas pure ZnO nanoparticles did not. The facile, bimetallic ZIF derived synthesis of doped-metal oxide nanoparticles can be used to design high-performance gas sensors.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.6
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• pp.123-132
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• 2012

Gas sensors has been used very differently that depending on following purposes; Automotive (exhaust gas, fuel mixture gas, oxygen, particulates), agriculture / food industry (fresh, stored, CO2, humidity, NH3, nitrogen oxide gas, organic gas, toxic gas emitted from pesticides and insecticides), industrial / medical (chemical gas, hydrogen, oxygen and toxic gases), military (chemical weapon), environmental measurements (CO and other air pollution consisting of sulfur and nitrogen gas), residential (LNG, LPG, butane, indoor air, humidity). The types of industrial toxic substances are known about 700 species and many of these exist in gaseous form under normal conditions. he multi-gas detection sensors will be developed for casualties that detect the most important and find easy three kinds of gases in marine plant; carbon dioxide(CO2), carbon(CO), ammonia(NH3). Package block consists of gas sensing device minor ingredient, rf front end, zigbee chip. Develope interworking technology between the sensor and zigbee chip inside a package. Conduct a performance test through test jig about prototype zigbee sensor module with rf output power and unwanted emission test. This research task available early address when poisonous gas leaked from large industrial site and contribution for workers' safety at the enclosed space.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.423-428
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• 2015

Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.72-76
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• 2009

The sensing system was designed and fabricated to investigate the ferment environment of soybeans. $NH_3$ gas was saturated after about 7 h and $CO_2$ gas was reached the peak after about 8 h in the inoculation of Bacillus subtilis. However, times that $CO_2$ gas and $NH_3$ gas were reached maximum value without Bacillus subtilis were about 15 h and 18 h, respectively. The sample that inoculated Bacillus subtils had deeper taste than one without it. We found that the peak time of $CO_2$ gas means the starting time of fermentation. If we control the operating time after the start of fermentation, it is expected to make a suitable Chungkukjang to individual preference.

• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.188-196
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• 1998

The sensing and electrical characteristics of $WO_{3}$-based n-type semiconductor gas sensors are investigated. In normal air condition, $TiO_{2}$(4 wt. %)-doped $WO_{3}$-based sensor fabricated without any binder shows the grain boundary ( GB ) potential barrier height of 0.26 V. Sensors fabricated with alumina, PVA and silica sol binders show 0.17, 0.22 and 0.26 V of GB potential barrier height, respectively. In the ambience of 120 ppm $NO_{x}$ concentration, the GB potential barrier height of the sensor fablicated without binder is increased to 0.59 V. The sensors were fabricated with alumina, PVA, silica sol binders show 0.43, 0.66 and 0.52 V of potential barrier, respectively. Thus the variation of the potential barrier at GB is largest in the sensor fabricated with the PVA binder. This is found to be the main reason why the sensor fabricated with the PVA binder shows the best sensitivity. It is also found that the decrease of sensitivity at a temperature higher than the optimum operation temperature is due to the temperature dependence of the sensor resistance in normal air condition rather than the desorption of the adsorbed $NO_{x}$ gas particles. In the ambience of 250 ppm CO concentration, the GB potential barrier heights of the sensors fabricated without binder and with PVA binder are about 0.2 V showing negligible change compared to the case of normal air ambience. This fact indicates that these sensors are good candidates for the selective detection of $NO_{x}$ gas in the mixture of CO and $NO_{x}$ gases.

• ETRI Journal
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• v.31 no.6
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• pp.636-641
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• 2009

ZnO nanofibers were electro-spun from a solution containing poly 4-vinyl phenol and Zn acetate dihydrate. The calcination process of the ZnO/PVP composite nanofibers brought forth a random network of polycrystalline wurtzite ZnO nanofibers of 30 nm to 70 nm in diameter. The electrical properties of the ZnO nanofibers were governed by the grain boundaries. To investigate possible applications of the ZnO nanofibers, their CO and $NO_2$ gas sensing responses are demonstrated. In particular, the $SnO_2$-deposited ZnO nanofibers exhibit a remarkable gas sensing response to $NO_2$ gas as low as 400 ppb. Oxide nanofibers emerge as a new proposition for oxide-based gas sensors.

• Journal of Sensor Science and Technology
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• v.26 no.3
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• pp.179-185
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• 2017

This article describes the characteristics of nondispersive infrared carbon dioxide gas sensor according to the temperatures and humidifies. In this researches, a thermopile sensor that included application-specific integrated circuit (ASIC) was used and the White-cell structure was implemented as an optical waveguide. The developed sensor modules were installed in gas chamber and then the temperature of gas chamber has been increased from 283 K to 313 K with 10K temperature step. In order to analyze the effects of humidity levels, the relative humidity levels were changed from 30 to 80%R.H. with small humidifier. Then, the characteristics of sensor modules were acquired with the increment of carbon dioxide concentrations from 0 to 2,000 ppm. When the initial voltages of sensors were compared before and after humidifying the chamber at constant temperature, the decrements of the output voltages of sensors are like these: 9mV (reference infrared sensor), 41 mV (carbon dioxide sensor), 2 mV (temperature sensor). With the increment of ambient temperature, the averaged output voltage of carbon dioxide sensor was increased 19 mV, however, when the humidity level was increased, it was decreased 14mV. Based upon the experimental results, the humidity effect could be alleviated by the increment of temperature, so the effects of humidity and temperature could be only compensated by the ambient temperature itself. The estimated carbon dioxide concentrations showed 10% large errors below 200 ppm, however, the errors of the estimations of carbon dioxide concentrations were less than ${\pm}5%$ from 400 to 2,000 ppm.

• Journal of Sensor Science and Technology
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• v.25 no.3
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• pp.173-177
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• 2016

Tape casting ceramics technology has been adopted for the fabrication of solid state electrochemical $CO_2$ sensors and the packaging substrates. The fabricated $CO_2$ sensors exhibit a fast response and a good recovery with the almost theoretical sensitivity of 37 mV/decade, corresponding to a sensor operating temperature of 373 K. The two packaging methods, the wire bonding package and the surface- mounted on the ceramic package, were compared with respect to their power consumption and mass production feasibility. In terms of the ease of fabrication, the surface mount packaging technology is superior to the wire bonding technology but its power consumption is approximately twice that of the wired package.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.210.2-210.2
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• 2014

Recently, molybdenum disulfide (MoS2) nanostructures have been investigated for applications of lithium-ion batteries, solar cell, and gas sensors. In this regard, we have studied atomic and electronic properties of MoS2 nanostructures with adsorbed atoms and molecules using density functional theory calculations. Our calculations reveal that the several atoms such as H, C, N, and F are chemically bound to several sites on the two-dimensional (2D) MoS2 surface. On the other hand, various contamination molecules such as CO, CO2, NO, NO2, and NH3 do not bind to the surface. Next, adsorption of various molecules on the one-dimensional (1D) armchair MoS2 nanoribbon is investigated. Contrary to the case of 2D MoS2 monolayer surface, some molecules (CO and NO) are bound well to the edge of the MoS2 nanoribbon. We find that the molecular states due to adsorption are located near the Fermi level, which makes the band gap narrower. Therefore, we suggest that monolayer MoS2 nanoribbons be used as the gas sensors or detectors.