A STUDY OF CUPC WATER INTERACTIONS USING SURFACE-ACOUSTIC-WAVE DEVICES

The aim of this paper is to report on the results obtained by a surfac e acoustic wave (SAW) technique used in measuring humidity sorption. D ual SAW delay-line oscillators are used. One of the two paths is coate d with an organic compound in order to achieve a gas sensor (copper ph thalocyanine, CuPC, for NO2 sensing). It appears, however, that if a p olar molecule is present in the vector ps (air or nitrogen) and sorbs on the SAW path, it can interact with these waves and modify the mecha nical and electrical fields. This results in Rayleigh wave velocity ch anges and as a consequence produces frequency shifts. Quartz substrate s (ST-cut, X propagating) are used for this study. Responses are obtai ned for many relative humidity values ranging from 0 to 90%. Each SAW delay-fine velocity change, as well as the difference between both of them, is monitored. We consider that mass loading is the most importan t effect (DELTAf = k DELTAm): water molecules induced only physical mo difications on both the organic layer and quartz substrate. This assum ption is reinforced by the cell time responses. A diffusion law is obv ious from the SAW oscillator frequency-transient analysis and measurem ents of the corresponding diffusion coefficients.