| With increasing application of hydrogen as one of the clean fuels and reduction gases, rapid and efficient leak-detection technologies have become a crucial problem during storage and use of hydrogen gas. In order to solve this problem, it is of great importance to develop safe, reliable and highly sensitive hydrogen sensors. Since palladium has been well known for its hydrogen-selective absorption, palladium-based composite films are widely used as hydrogen sensitive materials. In this thesis, we investigate the methods of electrodeposition and electroless plating to fabricate prime films on copper and wafer substrates, respectively. Different conditions were employed to control the morphology and thickness of these prime films. Then we fabricated the composite films by electrodepositing palladium films on the prime film. It is expected to enhance response speed and sensitivity of the hydrogen sensors through using large surface areas of the palladium films shaped by the prime film. Detailed investigations are as follows:Firstly, we used two kinds of plating solutions and different deposition time to deposit nickel nanoarrays and Co-Ni alloys on the copper substrate. It was found that, without CoCl2 in the plating solution, conical Ni nanostructures could be easily deposited on the copper. During early stage of the electrodeposition, height of the Ni nanocones is almost directly proportional to the deposition time. We found that a suitable deposition time was from 2 to 4 minutes. On the other hand, if CoCl2 was added into the plating solution, shell-like Co-Ni alloys could be fabricated. With increase of the deposition time, growth of the shell-like deposits becomes more evident. In addition, experimental results also indicated that we could obtain electroplated Ni nanocone arrays on the Ni-P coating.Secondly, we investigate how to fabricate Ni-P coatings by electroless plating method and Co-Ni alloys by electrodeposition method on silicon wafers. With increase of electroless plating solution temperature and pH value, growth of Ni-P particles was accelerated and the corresponding film could grow faster and thicker. After an electroless plating for 5minutes in the solution with a pH value of 7.5, we could fabricate a Ni-P coating with a thickness less than 3μm and only one layer of Ni-P particles were distributed on the wafer surface. The surface of wafer is not totally occupied by the Ni-P particles, which resulted in the formation of a porous structure. Therefore, we could draw a conclusion that porous Ni-P films could be gained only with low pH value and a deposition time less than 5 minutes. In addition, during an electrodeposition process of porous Co-Ni alloys, we could obtain optimized depositing conditions with a current density of 2.0A/dm2 and a deposition time of 2 minutes. Average diameter of the porous Co-Ni particle films is about 0.92μm.SEM and AFM analysis indicated that all of the above composite films have a large surface area. We also investigated the morphology variation of these films after a Pd electrodeposition. Due to an uniform cover on the prime films, Pd films could be shaped by the prime films and thus maintain a large surface area. However, an increase of deposition time could increase the thickness of Pd films. Thus, we recommend the use of an optimized deposition time of 15-20 seconds.
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