Document Type


Date of Award

Fall 10-31-1996

Degree Name

Master of Science in Applied Physics - (M.S.)



First Advisor

Ken K. Chin

Second Advisor

Kenneth Rudolph Farmer

Third Advisor

William N. Carr


Polycrystalline tin-dioxide is widely used in the detection of reducing gases (such as H2, CO, CH4, C2H5OH,...) in air by measuring its conductivity changes. The advantage of gas sensors based on such sensing devices is low cost and high sensitivity. In contrast to their widespread applications and to their successful empirical research and development work, the present understanding of the chemical sensing mechanisms is still immature.

In this thesis, for gas sensors based on thick and porous tin-dioxide layers, a study of the response function upon variation of the partial pressure of ethanol vapors in 100% humidified air has been carried out. The influence of the working temperature and of the water vapors on the conductivity of the sensor was particularly emphasized.

Based on our experimental data, a theoretical model of the sensing mechanism in thick and porous tin-dioxide layers is presented. The model accepts the conduction mechanism as being governed by the Schottky potential barriers at the junction between grains. For describing the adsorption of gas molecules on the solid surface a method of "conditioned adsorption" was developed. The central idea was to assume that the reducing gas molecules are "adsorbed" (i.e. react) only on pre-adsorbed oxygen. The predictions made in the frame of our theoretical model are in good agreement with the experimental data.

Included in

Other Physics Commons



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.