ULTRAFINE GRAIN-SIZE TIN-OXIDE FILMS FOR CARBON-MONOXIDE MONITORING IN URBAN ENVIRONMENTS

Various types of ultrafine grain-size SnO2 sensors have been fabricated using a reactive sputtering technique. Some have been doped using two different techniques: deposition (by sputtering) of a thin layer of platinum or platinum implantation. The samples are characterized using ellipsometry, ESCA/Auger spectroscopy, glancing angle XRD and RES. Sensor sensitivity measurements are carried out in the CO concentration range 5-100 ppm in dry air between 100 and 350 degrees C. For non-doped samples, the sensitivity is found to increase with temperature. The results obtained with the Pt-implanted sensors are variable and merit further investigation. The effects of the presence of low concentrations of NO2 in NO2/CO atmospheres have also been analyzed. It can be shown that a selective response to NO2 and CO/air mixtures can be achieved by a suitable choice of the sensor operating temperature.