Chemical sensors for gaseous species using oxide semiconductors

目前的研究项目是为了验证一种新的化学传感器方法的可能性，这种方法可以高选择性和高灵敏度地确定复杂气体混合物中化学物质的浓度。当施加稳态热脉冲时，该传感器可以测量由目标气体的化学吸附引起的表面电导率的变化，也可以测量由表面反应变化引起的不对称电池结构之间的混合电位。在本研究中，Nd_<2-x>Ce_xCuO_4（NCCO）主要研究其表面反应/吸附行为，因为它与NOx的反应活性非常高。本文采用直流极化和交流阻抗的方法，研究了Au (PO_2, PNO/PNO_2)/ nd_2o_3掺杂CeO_2/NCCO（P'O_2， P'NO/P'NO_2）的固态电化学电池，表征了NO+O^2=NO_2+2e‘（反应a）和O^<2->=1/O_2+2e’（反应B）的电荷转移反应。进一步讨论了电池混合电位的形成机理和电极/电解质界面上电荷转移的反应速率。此外，我们还进行了类似的实验，估计了在由YSZ电解质组成的电池上，Au、Pt和NiO电极的NO+1/O_2=NO_2反应（C反应）的总速率，并进行了比较。结果表明，混合电位在450℃左右达到最大值，催化效果在此温度范围内达到最大值。通过分析直流极化结果的Tafel图确定的交换电流密度，估计了电荷转移反应的速率。从讨论NO_2和利率的成分依赖性反应A和B,作者得出结论,之间的速率决定步骤是中途NO_2的竞争吸附,NCCO表面成分和表面电荷转移反应,也得出结论,混合可能是由于反应之间的反应速率的差异an4 B.Also检查进一步调查可能的候选人传感器组件,加工和制造技术，电子电荷在金属/氧化物界面上的转移和电子输运性质及其基于候选材料电子结构的解释。作为结论，已经证实了利用气体在特定氧化物上的化学吸附速率和活化能的差异来设计化学传感器的可能性。少

The present research project has been conducted to verify the possibility of a novel approach for chemical sensors to determine the concentration of chemical species in complex gas mixtures with high selectivity and sensitivity. The sensor proposed is to measure either change in the surface conductivity by the chemisorption of a target gas or the mixed potential build up between asymmetric cell configuration due to the change in the surface reactions, when steady-state ac heat pulse is applied. In the present study, Nd_<2-x>Ce_xCuO_4(NCCO)was mainly investigated for the surface reaction/adsorption behavior, due to the extraordinarily high reactivity with NOx. In the present study, the solid-state electrochemical cell written as Au (PO_2, PNO/PNO_2)/Nd_2O_3-doped CeO_2/NCCO(P'O_2, P'NO/P'NO_2)was examined by a dc polarization and ac impedance measurements, in order to characterize the charge transfer reactions of NO+O^2=NO_2+2e' (Reaction A) and O^<2->=1/O_2+2e'(Reaction B), and the dis … More cussion on the the mechanism was made for the build-up of the mixed potential across the cell and the reaction rate of the charge transfer at the electrode/electrolyte interface. In addition, similar experiments were made to estimate the overall rate of the reaction NO+1/O_2=NO_2(Reaction C)on the cells composed of YSZ electrolyte with Au, Pt and NiO electrodes for comparison. The present results indicated that the maximum values of the mixed potential were observed at around 450 C and that the catalytic effects showed maxima at this temperature range. The rate of the charge transfer reaction was estimated from the exchange current density determined by analyzing the Tafel plot on the results of dc polarization. From the discussion on the NO_2 and O_2 dependencies of the rates of reactions A and B, the author concluded that the rate determinant step lies midway between the the competing adsorption of NO_2 and O_2 on the NCCO surface and the the charge transfer reaction at the surface, it is also concluded that the mixed potential is caused by the difference in the reaction rates between reaction A an4 B.Also examined are further survey of the possible candidates for the sensor component, the processing and fabrication technique, the electronic charge transfer across the metal/oxide interface and electronic transport properties and their interpretation based on the electronic structure of the candidate materials.As a conclusion, it has been confirmed the possibility of the chemical sensor utilizing the difference in the chemisorption rate of gas species on a specific oxide and the activation energy. Less