We report the effect of the fabric of the surface microstructure on the CO gas sensing properties of SnO2 thin films deposited on self-assembled Au nanodots (SnO2/Au) that were formed on SiO2/Si substrates. We characterized structural and morphological properties, comparing them to those of SnO2 thin films deposited directly onto SiO2/Si substrates. We observed a significant enhancement of CO gas sensing properties in the SnO2/Au gas sensors, specifically exhibiting a high maximum response at 200˚C and quite a low detection limit of 1 ppm level in dry air. In particular, the response of the SnO2/Au gas sensor was found to reach the maximum value of 32.5 at 200˚C, which is roughly 27 times higher than the response (~1.2) of the SnO2 gas sensor obtained at the same operating temperature of 200˚C. Furthermore, the SnO2/Au gas sensors displayed very fast response and recovery behaviors. The observed enhancement in the CO gas sensing properties of the SnO2/Au sensors is mainly ascribed to the formation of a nanostructured morphology in the active SnO2 layer having a high specific surface-reaction area by the insertion of a nanodot form of Au nucleation layer.

Nano-sized SnO2 thick films were prepared by a screen-printing method onto Al2O3 substrates. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box as a function of the detection gas. The nano-sized SnO2 thick film sensors were treated in a N2 atmosphere. The structural properties of the nano SnO2with a rutile structure according to XRD showed a (110) dominant SnO2 peak. The particle size of SnO2:Ni nano powders at Ni 8 wt% was about 45 nm, and the SnO2 particles were found to contain many pores according to the SEM analysis. The sensitivity of the nano SnO2-based sensors was measured for 5 ppm CH4 gas and CH3CH2CH3 gas at room temperature by comparing the resistance in air with that in the target gases. The results showed that the best sensitivity of SnO2:Ni and SnO2:Co sensors for CH4 gas and CH3CH2CH3 gas at room temperature was observed in SnO2:Ni sensors doped with 8 wt% Ni. The response time of the SnO2:Ni gas sensors was 10 seconds and recovery time was 15 seconds for the CH4 and CH3CH2CH3 gases.

[ LaMeO3 ](Me = Cr, Co) powders were prepared using the polymeric precursor method. The effects of the chelating agent and the polymeric additive on the synthesis of the LaMeO3 perovskite were studied. The samples were synthesized using ethylene glycol (EG) as the solvent, acetyl acetone (AcAc) as the chelating agent, and polyvinylpyrrolidone (PVP) as the polymer additive. The thermal decomposition behavior of the precursor powder was characterized using a thermal analysis (TG-DTA). The crystallization and particle sizes of the LaMeO3 powders were investigated via powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and particle size analyzer, respectively. The as-prepared precursor primarily has LaMeO3 at the optimum condition, i.e. for a molar ratio of both metal-source (a : a) : EG (80a : 80a) : AcAc (8a) inclusive of 1 wt% PVP. When the as-prepared precursor was calcined at 700˚C, only a single phase was observed to correspond with the orthorhombic structure of LaCrO3 and the rhombohedral structure of LaCoO3. A solid-electrolyte impedance-metric sensor device composed of Li1.5Al0.5Ti1.5(PO4)3 as a transducer and LaMeO3 as a receptor has been systematically investigated for the detection of NOx in the range of 20 to 250 ppm at 400˚C. The sensor responses were able to divide the component between resistance and capacitance. The impedance-metric sensor for the NO showed higher sensitivity compared with NO2. The responses of the impedance-metric sensor device showed dependence on each value of the NOx concentration.

We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of 500˚C. It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at 250˚C and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

We investigated the effects of Co doping on the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with ZnO using pulsed laser deposition. Structural examinations clearly confirmed a distinct nanostructure of the CNTs coated with ZnO nanoparticles of an average diameter as small as 10 nm and showed little influence of doping 1 at.% Co into ZnO on the morphology of the ZnO-CNT composites. It was found from the gas sensing measurements that 1 at.% Co doping into ZnO gave rise to a significant improvement in the response of the ZnO-CNT composite sensor to NO gas exposure. In particular, the Co-doped ZnO-CNT composite sensor shows a highly sensitive and fast response to NO gas at relatively low temperatures and even at low NO concentrations. The observed significant improvement of the NO gas sensing properties is attributed to an increase in the specific surface area and the role as a catalyst of the doped Co elements. These results suggest that Co-doped ZnOCNT composites are suitable for use as practical high-performance NO gas sensors.

ZnO와 SnO2에 TiO2를 첨가시킨 ZnO-TiO2와SnO2-TiO2세라믹 복합체를 제작하여 1000ppm 일산화탄소에 대한 감응특성을 조사하였다. 상분석을 위해서 X-선 회절 분석을 하였고, 전자 주사 현미경을 이용해서 시편 파단면의 미세구조를 관찰했다. 일산화탄소 감도는 건조공기 분위기에서 측정한 저항(Rdry air )과 1000ppm 일산화탄소 분위기에서의 저항(Rco )을 측정하여 각각의 저항값의 비로 정의하였다. TiO2첨가에 의한 ZnO의 일산화탄소 감도의 변화는 ZT5의 경우 최대 감도가 약 1.7배 감소하였고, TiO 2첨가에 의한 SnO2의 일산화탄소 최대 감도는 약 2.5배 증가함으로써 비교적 ZnO-TiO2배 증가함으로써 비교적 ZnO-TiO2배 증가함으로써 비교적 ZnO-TiO2복합체 보다는 SnO2- TiO2복합체의 일산화탄소 감응특성이 우수했다.