Hydrogen absorption kinetics and optical properties of Pd-doped Mg thin films

Abstract

In order to develop optical fiber hydrogen sensors, thin film materials with a high optical contrast between the metallic and hydrided states are needed. Magnesium exhibits such a contrast but cannot be easily hydrogenated at room temperature. However, thin films of Pd-doped Mg (MgPdy with 0.023 ≤ y ≤ 0.125) prepared by magnetron dc sputtering can easily be hydrided at room temperature and 0.5 bar H2 within a few minutes. The rate of first hydrogenation increases linearly with increasing Pd concentration. Hydrogenation induces high variations of transmission (ΔT up to 20%) and reflection (ΔR up to 70%) of light (0.5 eV ≤ℏω≤6.0 eV corresponding to 2500 nm≥λ ≥ 210 nm). The optical properties can be understood by considering Pd as a deep donor in semiconducting MgH2.