Surface hydrogen–palladium studies using a new photopyroelectric detector

Abstract

A new hydrogen gas trace detection principle based on a photopyroelectric solid-state sensor has been developed. The sensor was made of thin commercially available polyvinylidene fluoride (PVDF) pyroelectric film, sputter coated with palladium (Pd). An infrared laser beam (800 nm) served to produce ac voltages due to the photopyroelectric effect. Exposure to hydrogen gas was shown to produce a differential signal between the Pd and reference electrodes. Accumulated experimental evidence has led us to tentatively attribute the detection principle to the adsorption, dissociation, and absorption of hydrogen molecules on the Pd surface, which caused a shift on the PVDF pyroelectric coefficient, due to electrostatic interactions of H+ ions with the PVDF polar molecular system at the Pd–PVDF interface. A quantitative interpretation of the hydrogen partial pressure dependence of the differential signal has been achieved using simple gas-solid interaction theory and the combination of the Langmuir isotherm with photopyroelectric theory. The new detector could become an excellent tool for surface science studies under ultrahigh vacuum, especially at low temperatures where other sensors do not exhibit good performance.