(Metallo)phthalocyanines as chemical interfaces on a surface acoustic wave gas sensor for nitrogen dioxide

Abstract

The response of a SAW (surface acoustic wave) gas sensor for NO/sub 2/ has been studied extensively by using NO/sub 2/ and a number of other gases (CO, CO/sub 2/, CH/sub 4/, NH/sub 3/, SO/sub 2/, H/sub 2/O, and toluene). Different metallophthalocyanines (MPC; M = H/sub 2/, Mg, Fe, Co, Ni, Cu, Pb) have been treated as a chemical interface on one delay-line of a dual delay-line oscillator. These compounds offer two sites for interaction, one at the metal ion (coordination complex formation) and one at the electron cloud in the periphery of the molecule (charge transfer complex formation). The results are discussed in terms of general performance characteristics. At 150/sup 0/C CoPC is preferred for selectivity and sensitivity and CuPC is preferred for response time. For CuPC the relation between sensitivity, layer thickness, and frequency (30-98 MHz) was calculated and also the effect of temperature (30-150/sup 0/C) was measured. PbPC cannot be used due to irreversible effects. The transaction mechanisms of these SAW chemosensors are a combination of changes in mass and in conductivity caused by several chemical and physical processes at the chemical interface.