Investigations on the resistance of the metal-free phthalocyanine and palladium bilayer sensor structure influenced by hydrogen

Abstract

Results concerning resistance measurements of two metal-free phthalocyanine (Pc) and palladium (Pd) bilayer sensor structures under the influence of medium hydrogen concentrations (0.5–4%) in nitrogen and air are presented. These two bilayer structures of different thicknesses of metal-free phthalocyanine (55 nm and 80 nm) and the same thickness of palladium (∼10 nm) have been realized in an electric system. For the interaction in nitrogen the bigger response has been observed in a sample with a thinner phthalocyanine layer. For interaction in air a change in the response character (increase–decrease of resistance) it is clearly visible in a sample with a thinner Pc film. Between 2% and 2.5% hydrogen concentration in air the structure of the palladium phase changes from α to β. The resistance of the α-Pd structure increases with the increasing hydrogen concentration whereas in the case of the β-Pd structure an opposite behavior is observed. Such a change is observed only concerning the interaction in air and for a thinner phthalocyanine (Pc) layer. In a structure with a thicker phthalocyanine film this phenomenon occurs at a higher hydrogen concentration.