Bi-layer nanostructures of CuPc and Pd for resistance-type and SAW-type hydrogen gas sensors

The copper phthalocyanine (CuPc thicknesses ∼80 nm, ∼100 nm and ∼200 nm) covered with ultra thin palladium layer (Pd thickness about 18 nm) has been studied in aspect of their application as bi-layer hydrogen gas-sensing nanostructures. The studies have been performed at low operating temperature range (30–38 °C). The investigated bi-layered structures were obtained by physical vapour deposition under vacuum conditions with application of LiNbO3 (Y- cut Z-propagating) and glass substrates. Then, the samples were tested by means of the surface acoustic wave and resistance methods. In order to characterize the surface topography the Atomic Force Microscopy has been applied. The characteristic frequency shifts have been observed after exposition to hydrogen. The absolute response value has been found to be dependent on the CuPc film thickness, the interaction temperature, hydrogen gas concentration. Investigations showed also that the bi-layer nanostructure with a 200 nm of CuPc is the most sensitive one. However, at the investigated interaction temperature ∼38 °C, the sensor characteristics are closest to linear dependence for the nanostructure with the 100 nm of CuPc. The simultaneously performed monitoring of the resistance and frequency changes provided observation of the acoustoelectric effect for the investigated nanostructures. The best sensitivity has been observed for the bi-layer structure with 100 nm of CuPc, which is characterized by the acoustoelectric parameter closest to 1.