Surface acoustic wave hydrogen gas sensor based on layered structure of palladium/metal-free phthalocyanine

A layered sensor structure of metal-free phthalocyanine H2PC (∼160 nm) with a very thin film of palladium (Pd20 nm) on the top, has been studied for hydrogen gas-sensing application at relatively low temperatures of about 30C and about 40C The layered structure was obtained by vacuum deposition (first the phthalocyanine Pc and than the Pd film) onto a LiNbO3Y- cut Z-propagating substrate, making use of the Surface Acoustic Wave method, and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of the planar resistance of the layered structure. In such a layered structure we can detect hydrogen in a medium concentration range (from 0.5 to 3% in air) even at about 30C At elevated temperature up to about 40C the differential frequency increases proportionally (almost linearly) to the hydrogen concentration and the response reaches its steady state very quickly. The response times are about 18 s at the lowest 0.5% hydrogen concentration to about 42 s at 4% (defined as reaching 100% of the steady state). In the case of the investigated layered structure a very good correlation has been observed between the two utilized methods - the frequency changes in the SAW method correlate quite well with the decreases of the layered structure resistance.