The modulation of thermoelectric power by chemisorption - A new detection principle for microchip chemical sensors

The differential thermopower (Seebeck effect) depends on the properties of two materials that form a junction. If one of the two materials is chemical ly sensitive, a thermocouple can constitute a chemical sensor that provides a chemically dependent signal similar to that of a chemically sensitive fi eld-effect transistor (CHEMFET). Thermocouples were fabricated from junctio ns of thin films of indium oxide (In2O3) and gold (Au) sputtered onto a gla ss substrate. The device, with the junctions Au-In2O3 and In2O3-Au was heat ed such that the two junctions were kept at slightly different temperatures . Thus, a thermoelectric voltage (Seebeck effect) was generated at the junc tions. When the device was exposed to a continuous flow of pure air or synt hetic air with traces of nitric oxide (NO2), the Seebeck voltage was found to he extremely sensitive to the NO2 contamination in the air, as expected from theory. We demonstrate the operation of a new chemical sensor that wor ks due to the modulation of the Fermi energy as a result of chemisorption. (C) 2000 The Electrochemical Society. S0013-4651(00)03-091-3. All rights re served.