Tin dioxide gas sensors. Part 2.—The role of surface additives
Tin dioxide gas sensors. Part 2.—The role of surface additives
复制标题
DOI：
10.1039/f19888400441
复制
发表时间：
1988
期刊：
影响因子：
--
通讯作者：
J. Mcaleer;P. Moseley;J. Norris;David E. Williams;B. Tofield
中科院分区：
文献类型：
--
作者：
J. Mcaleer;P. Moseley;J. Norris;David E. Williams;B. Tofield
这一点在之前已经得到证实（J. F。McAleer，P. T.莫斯利W. Norris和D. E.威廉姆斯，J.化学学会，法拉第trans.1，1987，83，1323），多孔二氧化锡颗粒的气体响应关键地取决于涉及吸附氧的电子表面状态，以及涉及待检测气体的燃烧反应速率。因此，可以预期的是，能够钉扎二氧化锡的费米能级或改变燃烧速率（取决于材料和温度的选择）的表面添加剂的使用将深刻地影响材料的气体传感器响应。发现情况确实如此。研究了表面添加贵金属和金属氧化物颗粒对二氧化锡气敏性能的影响。在接近环境的温度下使用贵金属在二氧化锡表面上施加了与氧无关的肖特基势垒，并导致对一氧化碳的明显低温响应，这可能是通过在贵金属上的吸附来改变表面电势（并因此改变肖特基势垒）。只有当分布在氧化物表面上的贵金属颗粒非常小（1-10 nm）时，才能预期这种特殊的效果：如果催化剂颗粒通过加热聚集，则该效果消失。外来氧化物（这里是Ag 2 O或ZnO）的颗粒在二氧化锡表面上的分布似乎也将表面能级固定到添加剂的表面能级，并且以这种方式处理的二氧化锡表现出被修改为类似于本体中的添加剂氧化物的气敏特性。在较高的温度下，特别是在贵金属催化剂的存在下，气体在样品的薄外壳内被完全氧化，因此颗粒的测量电阻对气体的响应消失。实际上，获得了对反应产物（H2O和CO2）的响应。
It has been shown earlier (J. F. McAleer, P. T. Moseley, J. O. W. Norris and D. E. Williams, J. Chem. Soc., Faraday Trans. 1, 1987, 83, 1323) that the gas response of porous pellets of tin dioxide depends crucially on electronic surface states involving adsorbed oxygen, and on the rates of combustion reactions involving the gases to be detected. It is expected, therefore, that the use of surface additives capable of either pinning the Fermi level of the tin dioxide or altering the rate of combustion (depending on choice of material and temperature) would profoundly affect the gas sensor response of the material. This is found to be the case. Studies of the influence of surface additions of precious metals and of metal oxide particles on the gas response behaviour of tin dioxide are described. The use of precious metals at temperatures near to ambient imposes an oxygen-independent Schottky barrier on the tin dioxide surface and results in a distinct low-temperature response to carbon monoxide, probably by adsorption on the precious metal modifying the surface potential (and hence the Schottky barrier). This particular effect is expected only when the precious metal particles distributed over the oxide surface are extremely small (1–10 nm): the effect disappears if the catalyst particles are aggregated by heating. The distribution of particles of a foreign oxide (here Ag2O or ZnO) on the surface of the tin dioxide also appears to pin the surface-energy levels to those of the additives, and tin dioxide treated in this way exhibits gas-sensing properties that are modified to resemble those of the additive oxide in bulk. At higher temperatures, especially in the presence of a precious-metal catalyst, the gas is completely oxidised within a thin outer shell of the specimen and consequently the response to the gas of the measured resistance of the pellet disappears. Indeed, a response to the reaction products (H2O and CO2) is obtained.