Basic Research for Development of Ceramic Odor Sensors

点击翻译按钮获取中文摘要

Sensing properties of semiconductor gas sensor were extensively improved by microstructrure control and by surface modification. A new design concept of semiconductor gas sensor was constructed in the present research.The sensitivity of snO_2 gas sensor was enhanced by controlling crystallite size (D) and thickness of space charge layer (L) of SnO_2 and the dispersion state of Pd promoter. The sensitivity increased with decreasing D close to 2L (=ca. 6 nm for pure SnO_2), while for Al^<3+>-doped SnO_2 it was very high even at large D because the doping brings about large L values. Therefore it was found that the sensitivity could be promoted when D/2L was controlled to be close to unity or less. On the other hand, the sensitivity of Pd-SnO_2 sensor was enhanced by highly dispersing small Pd particles on SnO_2 surface. The Pd complex fixation method was found to be the most excellent method to obtain the high dispersion of Pd particle.The improvement of the selectivity was attained by modifying the SnO_2 surface using foreign oxide additives. The sensitivity of SnO_2 gas sensor to ethanol gas was enhanced by adding basic oxide such as La_2O_3, probably because the oxidation of C_2H_5OH via dehydrogenation through CH_3CHO intermediate proceed favorably on the basic surface. Similar results were obtained for Pd-La_2O_3-In_2O_3 element effectively. On the other hand, CuO was a unique additives to enhance sensing properties of SnO_2 element to H_2S. CuO-SnO_2 element showed the extraordinary high sensitivity and selectivity, and switching-like recovery response on turning off H_2S. The change of state between CuO and CuS was found to be responsible for such unique sensing properties.