Impedance measurements of chemical gas sensors

This contribution deals with impedance measurements of gas sensors with active layers prepared by pulsed laser deposition (PLD) technology. The deposition was carried out from tin dioxide (SnO/sub 2/) and tin acetylacetonate (SnAcAc) - based targets by a KrF (wavelength 248 nm) excimer laser. The following systems were investigated (basic material/dopant/catalyst): SnO/sub 2/, SnAcAc, SnAcAc/Pd,SnAcAc/FeAcAc/Pd and SnAcAc/PdAcAc/Pd. These systems were applied as they exhibit an excellent S/sub dc/ sensitivity. The main interest was focused to following problems: measurement of real and imaginary part of complex impedance for frequencies ranging from 100 Hz to 10 MHz, construction of Nyquist diagrams, definition of an alternative phase-angle sensitivity S/sub pa/ (based on phase shift). The influences of S/sub pa/ vs. temperature and S/sub pa/ vs. frequency are also discussed.