Pd-Ni thin films grown on porous AL(2)O(3) substrates by metalorganic chemical vapor deposition for hydrogen sensing

Pd-Ni thin films were grown on porous substrates by metalorganic chemical v apor deposition (MOCVD) using the Pd- and Ni-acetylacetonate mixed precurso r. Porous alpha-Al2O3 disks with and without gamma-Al2O3 top layer deposite d 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 sur face morphology of the Pd-Ni thin film was determined by using scanning ele ctron microscope (SEM) and atomic force microscope (AFM). The porous substr ates have a remarkable effect on the film morphology, which contributes to different hydrogen sensing properties. The deposited film on a porous alpha -Al2O3 substrate was porous and discontinuous due to the large pores of the substrate used, and the sensitivity to hydrogen is significantly larger th an that of Pd-Ni thin film sensors reported in the literature. On the contr ary, the deposited film on porous gamma-Al2O3 surface with bright metallic mirror provided a more uniform and compact thin film, and the sensitivity t o hydrogen is much lower than that of the film on porous alpha-Al2O3 and bl isters are easily formed under hydrogen atmosphere. (C) 1999 Elsevier Scien ce S.A. All rights reserved.