THE INFLUENCE OF MORPHOLOGY ON THE RESPONSE OF IRON-OXIDE GAS SENSORS

Microgranular layers of iron oxide have been prepared by the depositio n of dried aerosol droplets of iron oxalate and subsequent decompositi on to investigate the gas-sensing properties of this special morpholog y. For comparison, compact iron-oxide films have been prepared by sput tering of iron and successive oxidation. Several different granular ga s detectors have been produced consisting of spherical particles with sizes between 0.2 and 1.2 mu m in narrow size distributions. Photoelec tron spectroscopy and secondary mass spectrometry are employed for dep th-resolved chemical analysis, showing Fe2O3 to be the major compound of both the compact and the granular layers. Methane, propane, benzene or toluene contained in dry air are used to test the response of the gas-sensitive films. No significant difference in the average sensitiv ity is found for the two sensor types. However, the selectivity and th e response time of the gas detectors show a considerable dependence on the morphology of the oxide layers. The compact films exhibit a prono unced sensitivity increase with molecular weight of the vapours. In co ntrast, the granular layers detect all gases with similar sensitivitie s and react faster than the compact layers.