Pd–Ni thin films grown on porous Al2O3 substrates by metalorganic chemical vapor deposition for hydrogen sensing

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Pd–Ni thin films were grown on porous substrates by metalorganic chemical vapor deposition (MOCVD) using the Pd- and Ni-acetylacetonate mixed precursor. Porous α-Al2O3 disks with and without γ-Al2O3 top layer deposited by a sol-gel process were employed as substrates. The composition of the films was very close to the Pd/Ni ratio in the mixed precursor as shown by X-ray photoelectron spectroscopy (XPS) analysis. The microstructure and surface morphology of the Pd–Ni thin film was determined by using scanning electron microscope (SEM) and atomic force microscope (AFM). The porous substrates have a remarkable effect on the film morphology, which contributes to different hydrogen sensing properties. The deposited film on a porous α-Al2O3 substrate was porous and discontinuous due to the large pores of the substrate used, and the sensitivity to hydrogen is significantly larger than that of Pd–Ni thin film sensors reported in the literature. On the contrary, the deposited film on porous γ-Al2O3 surface with bright metallic mirror provided a more uniform and compact thin film, and the sensitivity to hydrogen is much lower than that of the film on porous α-Al2O3 and blisters are easily formed under hydrogen atmosphere.