We developed a new technique for the deposition of free-standing porous sil
icon (PS) on alumina substrate with interdigital contacts (Italian Patent E
NEA-INFM), thus removing the silicon substrate, that is inactive in gas det
ection and is much more conductive than PS. The de and ac electrical measur
ements in a controlled atmosphere were performed to test the sensor respons
e towards NO2 (0.1-10 ppm), O-3 (200 ppb), CO (1000 ppm), benzene (20 ppm),
organic vapours and humidity. The device was able to detect very low conce
ntrations of nitrogen dioxide (100 ppb) with no interference from ozone, be
nzene, CO and organic vapours. Indeed humidity interferes with nitrogen dio
xide detection and must be kept under control. Since PS showed great respon
se to NO2 at room temperature (RT), no heating of the sensor is required. (
C) 2001 Elsevier Science B.V. All rights reserved.