STRUCTURE OF TIN OXIDE LAYERS AND OPERATING TEMPERATURE AS FACTORS DETERMINING THE SENSITIVITY PERFORMANCES TO NO(X)

Thin SnO2 layers have been prepared and characterized by ellipsometry, Auger spectroscopy, XPS and X-ray diffraction analysis for their thic kness and structure in order to be tested as NO, sensors. The experime nts were carried out both in pure nitrogen and in a nitrogen:oxygen (4 :1 vol.) mixture. The process of adsorption of NO2 on tin oxide result s in the build up of a carrier depletion layer and therefore a net dec rease of the electrical conductivity. In nitrogen:oxygen mixtures this process competes with those pertaining to the oxygen molecule. The ma ximum sensitivity for the detection of NO2 in an N2:O2 mixture was fou nd at approximately 210-degrees-C. This sensitivity position results f rom the minimum density of acceptors induced at this temperature by th e multistep oxygen ionosorption processes.