• Journal of Sensor Science and Technology
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• v.7 no.4
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• pp.254-262
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• 1998

Multilayer Langmuir-Blodgett (LB) films coated on quartz crystal microbalance (QCM) of octa-substituted metallophhtalocyanines ($MPc(OEH)_8$, M = Cu, Co, and Sn) and dihydrogen phthalocyanines ($H_2Pc(OEH)_8$) were used to quantify $NO_2$ concentrations. They were exposed to various concentrations of $NO_2$ in dry $N_2$. Among the four phthalocyanines we tested, the metal-free $H_2Pc(OEH)_8$ was observed to be most sensitive to $NO_2$. However, its LB film showed a partially irreversible behavior, that is part of the frequency change due to $NO_2$ adsorption could not be recovered even after purging with pure $N_2$ gas for an extended period. Examining the spectra of NMR and FTIR revealed fact that the irreversible portion of frequency change was due to ether groups in the linkage between side chains and the Pc unit. In order to remove the effect of such initial deactivation, on $NO_2$ quantification experiment, a freshly fabricated LB film was treated at a high concentration of $NO_2$ so that the ether sites were saturated. A pretreated LB film showed a reproducible performance for repeated uses. The $CuPc(OEH)_8$ LB film showed a satisfactory sensing performance down to as low as 4 ppm. For the $H_2Pc(OEH)_8$ LB film, the lower detection limit was found to be 35ppb of $NO_2$. In order to make the experimental condition more realistic, the carrier gas, dry nitrogen, was replaced by air. It was observed that the presence of oxygen, a weak electron acceptor, reduced the sensitivity and thus increased the sensing limit to hundreds of ppb. Results of experiments with moisture added showed that the interference of moisture was quite severe.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.241-246
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• 1998

It is well known for 410L ferritic stainless steel powder to applicate a sensor ring in anti-lock brake system of automobile, several studies, because of its excellent magnetic properties. This study was carried out to investigate the magnetic properties such as the maximum magnetic induction, coercivity and maximum permeability of the materials with functions of sintering density, time and temperature, and concluded as follows: 1. Sintering under the circumstances of Ar gas and the temperature of $1250^{\circ}C$ for 60min, showed that nitrogen was increased, whereas carbon and oxygen decreased in quantities. 2. Both maximum magnetic induction value of 4700Gauss and permeability of 200 were obtained at the maximum sintering density of $6.89g/cm^2$. Here, the properties showed a linear increasement with increasing the sintering density. 3. Coercivity sharply decreased with incresing the sintering density and reached to 7.6Oe at the maximum sintering density of $6.89g/cm^2$.

• Journal of Sensor Science and Technology
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• v.7 no.2
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• pp.117-123
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• 1998

The $In_{2}O_{3}$ thin films were fabricated on a alumina substrate by spin-coating method and the gas sensing properties were tested. The coating solution was synthesized by the mixing of aqueous solution of $In(OH)_{3}$ and acetic acid, and ammonium carboxymethyl cellulose as a binder. The $In_{2}O_{3}$ thin films between 71 and 210nm thick were obtained by spin-coating between 1 and 7 times followed by drying at $110^{\circ}C$ and calcining at $600^{\circ}C$. The films consisted of a dense stack of tiny $In_{2}O_{3}$ particles between 23 and 27nm in diameter and covered well large grains of the alumina substrate. Then film thickness was well controlled by the number of spin-coating. The fabricated $In_{2}O_{3}$ films showed high sensitivity and very fast response property to CO and $H_{2}$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.250-251
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• 2014

This study introduces a simple deposition of $Cu_2O$ thin films with surface morphologies composed of columns, submicron-rods and submicron-branches on glass substrate from metallic Cu targets by tailoring the $Ar/O_2$ ratios during the sputtering. The obtained samples were used to fabricate gas sensor. The $H_2S$ sensing properties of the sensors at working temperatures from $100^{\circ}C$ to $300^{\circ}C$ were studied, in which $Cu_2O$ submicron-branches performed the best sensing property comparing with the rest morphologies. A transformation of $Cu_2O$ to $Cu_2S$ and CuS was consider as a main factor to the sensing mechanism of the sensors.

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.61-67
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• 1996

The growth and characterization of heteroepitaxial $Si_{1-x}Ge_{x}$ films grown by the RTCVD (Rapid Thermal Chemical Vapor Deposition) method were described. For the growth of $Si_{1-x}Ge_{x}$ heteroepitaxial layers, $SiH_{4}$ / $GeH_{4}$ / $H_{2}$ gas mixtures were used. The growth conditions were varied to investigate their effects on the Si / Ge composition ratios, the interface abruptness and crystalline properties. The experimental data shows that the misfit threading dislocation in $Si_{1-x}Ge_{x}$ / Si heteroepitaxial film of about $400\;{\AA}$ thickness was not observed at the growth temperature of as low as $650^{\circ}C$, and the composition ratios of Si / Ge changed linearly with $SiH_{4}$ / $GeH_{4}$ gas mixing ratios in our experimental ranges. In the in-situ boron doping experiments, the doping abruptness would be controlled within several hundreds ${\AA}$/decade.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1867-1869
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• 2003

In this paper, chamber(Circuit breaker compartment of C-GIS) made of stainless steel with 4 mm width is used. Artificial defect was made on enclosure or HV conductor of chamber and $SF_6$ gas was injected into it according to pressure. In this experiment, Acoustic emission sensors of different types was used to compare sensitivity to detect acoustic signal occurred by Partial discharge(PD) of according to types and resonance frequency in $SF_6$ gas atmosphere. Sensors used in tests was R6I, R15I and 2/4/6 Pre-Amplifier connected with R6IU without pre. amp. In case of R6IU, gain was adjusted with 40 dB like other sensors and operated by differential mode. Post amplifier(post. amp) and band pass filter(BPF) were developed Gain of post. amp. is 60 dB and BPF has band width of $50{\sim}300$ kHz. Also, envelope circuit developed reduces frequency of AE sensor. As a result, in $SF_6$ atmosphere, R6IU and R6I had resonance frequency of 60 Hz was better than R15I. Also, R6IU was better than R6I because of type property of pre.amp. had differential mode.

• Journal of Sensor Science and Technology
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• v.33 no.5
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• pp.318-325
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• 2024

In this study, we fabricated TiO₂-decorated SnO₂ nanorods (TSNRs) via glancing-angle deposition to achieve highly sensitive and selective CH₃COCH₃ detection. The gas-sensing properties of the TSNRs were systematically investigated, and the optimal sensing performance was achieved at 350℃ by 2-nm-thick TSNRs. When the sensors were exposed to 50 ppm of various gases (CH₃COCH₃, C₂H₅OH, C₅H₈, CH₄, and CO), the 2-nm-thick TSNRs demonstrated a 4.6-fold increase in response (R_a/R_g-1=134) to CH₃COCH₃ compared with bare SnO₂ nanorods (R_a/R_g-1=29.5) and exhibited excellent selectivity. In a high-humid environment (relative humidity = 80%), the 2-nm-thick TSNRs indicated a low theoretical detection limit of ≈5.31 ppb for CH₃COCH₃. These results suggest the significant potential of the proposed sensor for use in Internet-of-Things applications, particularly under extreme environmental conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.212-212
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• 2013

본 연구에서는 최근 다양한 전자 소자로써의 연구가 진행되고 있는 그라핀을 실리콘 기판위에 전자빔 식각(Electron-Beam Lithography)을 이용하여 TLM (Transfer Length Method) 패턴을 형성하고 가스 유입이 가능한 진공 챔버를 가지는 Probe Station을 이용하여 I-V 변화를 측정함으로써, 그라핀을 가스 센서 소자로서의 가능성을 연구하였다. 우리는 기존의 광식각을 이용한 TLM 패턴 형성과 더불어 전자빔 식각(E-Beam Lithography: EBL)을 이용한 TLM 패턴을 형성하여 I-V를 측정하였는데, 전자빔을 이용한 TLM 패턴의 형성은 광식각을 이용한 방법에 비해 더 세밀하고 미세한 패턴을 형성하는 것이 가능하다. 이렇게 형성된 그라핀의 TLM패턴은 가스 유량 조절이 가능한 진공 챔버를 가지는 Probe Station을 이용하여 측정하게 되는데, 이 때 저진공 상태의 챔버 내로 N2, H2 두 종류의 가스를 각각 유량을 변화시키며 주입하고 그 변화를 측정하였다. 유입된 가스는 그라핀의 Dangling Bond에 결합됨으로써 그라핀의 전도도를 변화시키게 되고, 변화된 그라핀의 전도도에 따른 I-V 결과의 변화를 측정하여 이를 가스 센서로 사용할 수 있는지를 측정하였다. 또한 유입되는 가스의 유량 변화에 따른 I-V 결과의 변화량을 통하여 가스 센서의 민감도 또한 측정하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.71-83
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• 2013

Recently, the advanced condition monitoring methods such as the model-based method and the artificial intelligent method have been applied to maximize the availability as well as to minimize the maintenance cost of the aircraft gas turbines. Among them the non-linear GPA(Gas Path Analysis) method and the GA(Genetic Algorithms) have lots of advantages to diagnose the engines compared to other advanced condition monitoring methods such as the linear GPA, fuzzy logic and neural networks. Therefore this work applies both the non-linear GPA and the GA to diagnose AE3007 turbofan engine for an aircraft, and in case of having sensor noise and bias it is confirmed that the GA is better than the GPA through the comparison of two methods.

• Korean Journal of Metals and Materials
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• v.47 no.6
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• pp.372-377
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• 2009

We report on hysteresis behavior in the electrical resistance-hydrogen concentration of Pd thin films. The variation of the electrical resistance has been investigated during the process of absorption and desorption of hydrogen gas ($H_{2}$) as a function of thickness of Pd thin films. The hysteresis behavior in the electrical resistance with $H_{2}$ concentration was found for Pd thin films and consists of $\alpha$ phase, ${\alpha}+{\beta}$ phase, and $\beta$ phase regions. The sensitivity of Pd thin films with $H_{2}$ concentration was found to follow Sieverts' law in the $\alpha$ phase region. However, the sensitivity was observed to increase abruptly with $H_{2}$ concentration in the ${\alpha}+{\beta}$ phase co-exist region. This is because Pd-H interaction is stronger in the $\beta$ phase than in the $\alpha$ phase and needs a higher concentration gradient as a driving force to desorb. The formation of the $\beta$ phase also was observed to cause the structural change because of the lattice expansion during absorption. The hysteresis height and the trace of structural change were affected by the thickness of the Pd film. As the film becomes thinner, the hysteresis height becomes lower and the amount of delamination on the surface becomes smaller. For films thinner than 20 nm in thickness, the delamination was not found but electrical resistance hysteresis was still observed.