An Analysis of Surface Reaction of Gas Sensors

通过对气体传感器表面反应的实验结果和模拟结果进行比较，实现了气味识别传感器。羧酸气体、酒精气体和氨基气体作为样品气体。用MOPAC97包程序进行分子轨道计算，计算了SnO_2团簇和气体样品的形成热和表面电荷随团簇与气体分子之间距离的函数关系。计算结果表明，醋酸气体是一种羧酸气体，其吸附距离比醇类气体和胺类气体更接近SnO_2簇表面，吸附距离为5 a。该传感器对羧酸类气体的灵敏度高于胺类气体。这些结果表明，与SnO2表面的吸附距离对传感器的灵敏度有很大影响。我们还测量了气体传感器在传感器加热器调制下对几种酒精气体的响应。不同类型的酒精气体具有不同的三角形电压调制。反应的延迟时间在不同的酒精气体中有所不同。当传感器用三角形电压调制时，差异达到最大，其增加速度为43 mV/sec。通过传感器加热器调制，对甲醇、乙醇、丙醇和丁醇四种酒精气体进行了区分。

We have compared experimental results and simulated results for surface reaction on a gas sensor to realize smell distinguishable sensor. Carboxylic acid gases, alcoholic gases and aminic gases were used as sample gases. Heat of formation and surface charge of an SnO_2 cluster and sample gases were estimated as a function of the distance between the cluster and gas molecules by molecular orbital calculation with MOPAC97 package. The calculation results showed that acetic acid gas, a kind of carboxylic acid gas, was adsorbed closer than alcoholic and aminic gases to the SnO_2 cluster surface with a distance of 5 A. Sensitivity of the gas sensor for carboxylic acid gases was higher than that of aminic gases. These results suggested that the adsorption distance from the SnO2 surface strongly affected the sensor sensitivity.We have also measured responses of a gas sensor for several alcoholic gases under modulation of sensor heater. The responses were dependent on kinds of alcoholic gases with different triangular shaped voltage modulation. Delay times of the responses were differing among alcoholic gases. The differences reached the maximum when the sensor was modulated with a triangular voltage with its increasing speed of 43 mV/sec. Four kinds of alcoholic gases, which were methanol, ethanol, propanol and butanol, were distinguished by sensor heater modulation.