Surface acoustic wave (SAW) devices are very attractive as gas sensors
due to high sensitivity and low cost. Polypyrrole, obtained by a soli
d reaction from a ferric stearate Langmuir-Blodgett (LB) film, has bee
n deposited onto 128 degrees YX-LiNbO3 substrate in order to implement
a SAW chemical sensor. The formation of the conducting polymer has be
en confirmed by X-ray photoelectron spectroscopy (XPS), secondary ion
mass spectrometry (SIMS) and scanning electron microscopy (SEM) measur
ements. The SAW delay line, equipped by interdigital transducers opera
ting at a frequency of 42 MHz and coated by a sensitive polypyrrole LB
film, has been tested towards NH3 gas in air. Due to the absorption p
rocess, the various loadings cause a variation of acoustic wave veloci
ty measured by the phase shift technique at the output of SAW device.
Partially reversible SAW acoustic response towards NH3 in air has show
ed high sensitivity. The calibration curve towards NH3, its detection
limit and degradation phenomena of the coating have been performed. Ou
r LB polypyrrole SAW detector exhibits excellent selectivity towards N
H3. (C) 1998 Elsevier Science S.A. All rights reserved.