Surface Acoustic Wave Hydrogen Sensor with Nickel Phtalocyyanine and Palladium Thin Layers

Presented here are the results concerning a hydrogen sensor based on a novel bilayer structure in a Surface Acoustic Wave dual-delay line system. The sensor material consists of two layers produced in two different vapour deposition processes.The first one is a 230 nm nickel phtalocyanine (NiPc) layer, whereas the second is a 20 nm thin palladium (Pd) film. This structure was formed in one of the dual delay line systems on a LiNbO3 Y-cut Z-propagation substrate, while the other serves as a reference, permitting an easy detection of the arising differential frequency ?f. This frequency, depending on the operating frequency modes, is in range of 20 to 30 kHz, whereas he oscillator frequencies are in the range of 43.6MHz. The wavelenghts is 80um. In such a bilayer structure detection of hdrogen in a medium concentration range (from 1% to 4% in nitrogen) is possible, even at room temperature. For the investigated structure the interaction response depends on temperature. For the structure an interesting "interaction jump" has beeen detected, which is connected wht the phase trasition in the palladium film. At hidher temeperatures thisinteraction jump shifts in the direction of higher hydrogen concentrations.