Nano-indium-coated ZnO:In thick films were prepared by a hydrothermal method. ZnO:In gas sensors were fabricated by a screen printing method on alumina substrates. The gas sensing properties of the gas sensors were investigated for hydrocarbon gas. The effects of the indium concentration of the ZnO:In gas sensors on the structural and morphological properties were investigated by X-ray diffraction and scanning electron microscopy. XRD patterns revealed that the ZnO:In with wurtzite structure was grown with (1 0 0), (0 0 2), and (1 0 1) peaks. The quantity of In coating on the ZnO surface increased with increasing In concentration. The sensitivity of the ZnO:In sensors was measured for 5 ppm CH4 gas and CH3CH2CH3 gas at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity to CH4 gas and CH3CH2CH3 gas of the ZnO:In sensors was observed at the In 6 wt%. The response and recovery times of the 6 wt% indiumcoated ZnO:In gas sensors were 19 s and 12 s, respectively.

ZnO nanorods for gas sensors were prepared by a hydrothermal method. The ZnO gas sensors were fabricated on alumina substrates by a screen printing method. The gas-sensing properties of the ZnO nanorods were investigated for CH4 gas. The effects of growth time on the structural and morphological properties of the ZnO nanorods were investigated by X-ray diffraction and scanning electron microscope. The XRD patterns of the nanocrystallized ZnO nanorods showed a wurtzite structure with the (002) predominant orientation. The diameter and length of the ZnO nanorods increased in proportion to the growth time. The sensitivity of the ZnO sensors to 5 ppm CH4 gas was investigated for various growth times. The ZnO sensors exhibited good sensitivity and rapid response-recovery characteristics to CH4 gas, and both traits were dependent on the growth time. The highest sensitivity of the ZnO sensors to CH4 gas was observed with the growth time of 7 h. The response and recovery times were 13 s and 6 s, respectively.

A novel electrode for an NO gas sensor was fabricated from electrospun polyacrylonitrile fibers by thermal treatment to obtain carbon fibers followed by chemical activation to enhance the activity of gas adsorption sites. The activation process improved the porous structure, increasing the specific surface area and allowing for efficient gas adsorption. The gas sensing ability and response time were improved by the increased surface area and micropore fraction. High performance gas sensing was then demonstrated by following a proposed mechanism based on the activation effects. Initially, the pore structure developed by activation significantly increased the amount of adsorbed gas, as shown by the high sensitivity of the gas sensor. Additionally, the increased micropore fraction enabled a rapid sensor response time due to improve the adsorption speed. Overall, the sensitivity for NO gas was improved approximately six-fold, and the response time was reduced by approximately 83% due to the effects of chemical activation.

Recently, one-dimensional semiconducting nanomaterials have attracted considerable interest for their potential as building blocks for fabricating various nanodevices. Among these semiconducting nanomaterials,, SnO2 nanostructures including nanowires, nanorods, nanobelts, and nanotubes were successfully synthesized and their electrochemical properties were evaluated. Although SnO2 nanowires and nanobelts exhibit fascinating gas sensing characteristics, there are still significant difficulties in using them for device applications. The crucial problem is the alignment of the nanowires. Each nanowire should be attached on each die using arduous e-beam or photolithography, which is quite an undesirable process in terms of mass production in the current semiconductor industry. In this study, a simple process for making sensitive SnO2 nanowire-based gas sensors by using a standard semiconducting fabrication process was studied. The nanowires were aligned in-situ during nanowire synthesis by thermal CVD process and a nanowire network structure between the electrodes was obtained. The SnO2 nanowire network was floated upon the Si substrate by separating an Au catalyst between the electrodes. As the electric current is transported along the networks of the nanowires, not along the surface layer on the substrate, the gas sensitivities could be maximized in this networked and floated structure. By varying the nanowire density and the distance between the electrodes, several types of nanowire network were fabricated. The NO2 gas sensitivity was 30~200 when the NO2 concentration was 5~20ppm. The response time was ca. 30~110 sec.

Titanium dioxide thin films were fabricated as hydrogen sensors and its sensing properties were tested. The titanium was deposited on a SiO2/Si substrate by the DC magnetron sputtering method and was oxidized at an optimized temperature of 850˚C in air. The titanium film originally had smooth surface morphology, but the film agglomerated to nano-size grains when the temperature reached oxidation temperature where it formed titanium oxide with a rutile structure. The oxide thin film formed by grains of tens of nanometers size also showed many short cracks and voids between the grains. The response to 1% hydrogen gas was ~2×106 at the optimum sensing temperature of 200˚C, and ~103 at room temperature. This extremely high sensitivity of the thin film to hydrogen was due partly to the porous structure of the nano-sized sensing particles. Other sensor properties were also examined.

Ru-C nano-composite films were prepared by MOCVD, and their microstructures and their electrode properties for oxygen gas sensors were investigated. Deposited films contained Ru particles of 5-20 nm in diameter dispersed in amorphous C matrix. The AC conductivities associating to the interface charge transfer between Ru-C composite electrode and YSZ electrolyte were 100-1000 times higher than that of conventional paste-Pt electrodes. The emf values of the oxygen gas concentration cell constructed from the nano-composite electrodes and YSZ electrolyte showed the Nernstian theoretical values at low temperatures around 500 K. The response time of the concentration cell was 900 s at 500 K.

Metallic tin powder with diameter less than 50 nm was synthesized by inert gas condensation method and subsequently oxidized to tin oxide () along the two heat-treatment routes. The powder of single phase with a tetragonal structure was obtained by the heat-treatment route with intermediate annealing step-wise oxidation, whereas the powder with mixture of orthorhombic and tetragonal phases was obtained by the heat-treatment route without intermediate annealing (direct oxidation). gas sensors fabricated from the nano-phase powders were investigated by structural observations as well as measurement of electrical resistance. The gas sensors fabricated from the mixed-phase powder exhibited much lower sensitivity against gas than those fabricated from the powder of tetragonal phase. Reduced sensitivity of gas sensors with the new orthorhombic phase was attributed to detrimental effects of phase boundaries between orthorhombic and tetragonal phases and many twin boundaries on the charge mobility.

이산화탄소 기체센서를 Li2ZrO2계에서 온도와 CO2농도의 함수로서 연구했다. Li2ZrO3를 열처리해서 합성했다. 시편은 직경 10mm, 두께 1mm의 벌크형과 알루미나 기판 위에 후막형으로 각각 제조했다. Li2ZrO3는 450˚C에서 650˚C의 온도 범위에서 0.1%에서부터 100%까지 이산화탄소 농도 변화를 감지한다. 이산화탄소 감도는 측정온도와 연관성이 있다. Li2ZrO3는 450˚C에서 650˚C의 온도 범위에서 CO2와 반응해서 Li2CO3와 ZrO2로 분해된다. 650˚C 이상에서 Li2CO3는 Li2O와 CO2로 재분해된다. Li2ZrO3센서의 재현성은 좋지 않았고, 동작온도는 550˚C 정도가 적당하였다.

박막 형 가스 센서의 막 두께가 가스 감지 특성에 미치는 영향을 단순화된 모델로부터 수식으로 유도하여 해석하였고, 그것을 SnO2와 CuO-SnO2 박막의 h2S 감응 특성에 대한 실험 결과에 적용하였다. 유도된 수식으로부터 박막 가스 센서의 가스 감지 특성은 가스의 박막 안으로의 확산성에 크게 의존하며, 그 가스 확산성은 박막의 두께, 가스의 센서 재료의 반응성, 작동 온도 등에 의해서 결정됨을 알 수 있었다. 또한 이 수식은 CuO-SnO2 박막의 h2S 감응 특성에 대한 실험 결과와 비교적 잘 일치하였고, CuO-SnO2 박막과 SnO2 박막의 서로 판이한 h2S 감응 특성에 대한 설명에 적용되었다. 이로부터, 일반적인 산화물 반도체식 가스 센서의 가스 감지 특성이 가스 확산성에 의해서 어떻게 지배되는가를 구체적으로 제안하였다.

Ultra thin films of Tetra-3-hexadecylsulphamoylcopperphthalocyanine(HDSM-CuPc) were formed on various substrates by Langmuir-Blodgett method, where HDSM-CuPc was synthesized by attaching long-chain alkylamine(hexa-decylamine) to CuPc. The reaction product was identified with FT-IR, UV-visible absorption spectroscopies, elemental analysis and thin layer chromatography. The formation of Ultrathin Langmuir-Blodgett(LB) films of HDSM-CuPc was confirmed by FT-IR and UV-visible spectroscopies. A quartz piezoelectric crystal coated with LB films of HDSM-CuPc was examined as a gas sensor for N02 gas. HDSM-CuPc LB films were transferred to a quartz crystal microbalance(QCM) in the form of Z-type multilayers. Response characteristics of film-coated QCM to NO2 gas concentrations over a range of 100~600ppm have been tested with a thickness of 5~20 layers of HDSM-CuPc. Changes in frequency by adsorption of NO2 were increased With the number of LB layers and NO2 concentration, but the response time was slow.

수산화물법에 의해 제작된 α-stannic acid의 열분해 거동과 SnO2분말의 성질에 미치는 잔류염소이온의 영향을 관찰하였다. SnCl4와 NH4OH 수용액을 중화시켜 α-stannic acid침전물을 제작하고 NH4NO3수용액으로 세척하였다. 분말내의 잔류 염소이온의 양을 주절하기 위하여 세척정도를 3단계로 조정하였다. 세척후 100˚C에서 건조하고, 500˚C ~ 1100˚C에서 하소함으로써 SnO2분말을 제조하였다. α-stannic acid의열분해 거동ㅇ르 DT-TGA 와 FTIR을 통하여 관찰하고, SnO2분말의 조성과 입자크기 및 비표면적을 각각 AES, TEM 및 BET을 통하여 측정하였다. 잔류 염소이온 양이 감소되면, 저온 하소시 일차입자의 상대적 크기가 커지는 반면 고온하소시에는 상대적으로 감소되었ㄷ. 잔류 염소이온의 일부는 α-stannic acid내의 격자산소 자리에 위치함으로써, 저온가열시 결정수탈리와 결정화를 지연시키고 또한 고온가열시에는 이의 증발에 의해 산소공공이 생성되어 소결을 촉진시킨다고 제의하였다.

이 논문은 SnO2에 소량의 Pd를 첨가하여 이것을 Al2O3기판위에 진공증착시켜 가스소자를 제작한 후, 소자의 감지특성에 영향을 미치는 열처리 온도, 소자의 온도, Pd의 첨가량의 변화 효과를 조사한 것이다. 소자의 열처리 온도가 550˚C일때와 소자의 동작온도가 350˚C일때 ethanol gas에 접촉시 소자 저항이 가장 낮았다. Pd 1 wt%를 첨가한 경우 에탄올 가스에 대한 소자의 감지특성이 가장 양호하였으며, 저농도 영역에서 특히 우수하였다.