A porous silicon-palladium composite film for optical interferometric sensing of hydrogen

Porous Si Fabry-Pérot films are coated with Pd via immersion plating. The materials are characterized by electron microscopy and infrared spectroscopy. The Pd-coated porous Si samples exhibit distinct Fabry-Pérot fringes in the optical reflection spectrum due to thin film optical interference in the porous Si layer, though the reflectivity spectrum loses fidelity upon Pd coating. The effect of H2 exposure on the interference spectrum is studied. Absorption of hydrogen into Pd induces a lattice expansion, which results in a shift of the optical fringes and a decrease in the reflected intensity. The detection limit measured at room temperature is approximately 0.2% (by volume) in an N2 carrier gas, with a response time of a few seconds.