Study On The Preparation Of Nanoporous Pd Films And Pd-Ag Composite Films And Their Hydrogen Sensing Properties At Room Temperature

Hydrogen（H₂）gas,as a clean energy source,has been widely used in many fields,such as medical,petrochemical,electronics,aerospace and nuclear power plant.However,hydrogen gas is flammable and explosive with a Lower Explosive Limit（LEL）of 4.65%in air at room temperature.Therefore,hydrogen sensor with a fast response,safe and reliable has important significance.Palladium（Pd）is a good hydrogen storage material,as well as common hydrogen sensitive material in the hydrogen sensor field.Aim to the problems such as slow response speed and hydrogen embrittlement of the traditional Pd thin film sensors,nanoporous structural Pd and Pd-Ag composite thin films on silicon（Si）substrates were achieved through DC sputtering technique and the following annealed process in this paper.The influence of annealing temperature on phase morphology of nanoporous structural Pd film and its hydrogen sensing performance at room temperature were investigated,and the working mechanism of the sensors was also analyzed.Finally,hydrogen sensing properties of Pd-Ag composite thin films at room temperature was also studied.The main research results can be summarized as follows:1.Nanoporous structural Pd thin films were prepared through DC sputtering technique and the following annealed process.Nanoporous structural Pd thin films with different morphology were obtained by controlling sputtering parameters and the annealing temperature.The results showed that the phase of the sample after annealed at 200℃ to 400℃ did not change.The diffraction peak intensity of Pd increased with the increase of annealing temperature.The sample was gradually transformed from Pd thin film into nanoporous structural Pd thin films.And the RMS surface roughness of the samples was gradually increased when the annealing temperature was increased to 400℃ and then dispersive Pd nano-particles were obtained.2.A simple hydrogen sensor device was made by using a metal mask to prepare the nanoporous structural Pd.thin films on the Pt electrode with the interspacing of 5 mm.The nanoporous structural Pd thin films after heating treatment in vacuum had larger specific surface area and stronger hydrogen adsorption ability than the Pd thin films without heating treatment and can accelerate the rate of hydrogen adsorption and desorption,which can improve the response and recovery rate.The nanoporous structural Pd thin films exhibited more excellent response performance.The hydrogen detection was very fast and sensitive.The response time was about 12s and the sensitivity was up to 20%.The sensor had good repeatability,stability and selectivity.3、Pd-Ag composite thin films were prepared through DC sputtering technique and the following annealed process on the basis of the nanoporous structural Pd thin films preparation.We studied the microstructure and hydrogen sensing performance at room temperature.The results showed that the addition of appropriate amount of Ag could effectively improve the deficiency of slower response speed,hydrogen embrittlement and other defects in the traditional Pd thin films.Although the Pd-Ag composite thin films sensors exhibited low sensitivity to 0.8%hydrogen concentration,the sensors showed fast response time of～9 s and good repeatability,which has significant meaning for the practical application of Pd based sensors.