Electrical and optical responsivity of thin palladium films during hydrogen exposure
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1098-HH08-04
Electrical and optical responsivity of thin palladium films during hydrogen exposure Susan K Earles, Kanthi Yalamanchili, Ivica N Kostanic, Mohammed Nazer, Maria Pozo de Fernandez, and Mary H McCay Florida Institute of Technology, 150 W University Blvd, Melbourne, FL, 32901 ABSTRACT This paper presents a series of measurements documenting changes in electrical and optical properties of thin palladium films. Palladium is deposited on the glass surface through plasma-assisted physical vapor deposition. This process produces highly uniform films with a surface variation of a few nanometers. The thicknesses of studied films range from 15 to 60 nm. The films are exposed to a constant flow of 2% hydrogen and 98% nitrogen mixture. During the exposure, film resistivity and its reflection properties in visible light were monitored. It is observed that the change in the film resistance during the hydrogen exposure depends on the film thickness. In particular, thicker depositions exhibit larger relative changes of the resistance. The reflectivity of the films in the white light changes during the hydrogen exposure as well. However, the change of the film reflectivity is observed to be independent of the deposition thickness. This paper presents observed measurements, their quantitative analysis and briefly discusses the use of findings in development of low-cost, single-use commercial grade hydrogen sensors. INTRODUCTION The need for clean energy is fueling research in hydrogen based technologies. Cheap and reliable hydrogen sensors built on the basis of readily available processes are needed for deployment of hydrogen technology into the commercial environment. Hydrogen becomes flammable in air at concentrations greater than 4% and requires very little energy for ignition. Therefore, development of good hydrogen sensors is a prerequisite for widespread use of the hydrogen based technologies. In development of such sensors one may utilize materials whose properties change in the presence of hydrogen. There are many researchers investigating how to make sensors that have high sensitivities to low hydrogen concentrations. They are generally investigating complex structures based on MOS or diodes that rely on expensive processing facilities. These sensors often incorporate palladium (Pd) into their structure as it is well known that its electrical properties change in the presence of hydrogen [1-8]. In order to show the benefit of the more complex MOS and diode based sensors, the simple resistor based sensor similar to Antonangeli’s work [8] will be characterized. This work reports on the use of thin Pd films to make simple, low cost hydrogen sensors. This paper presents changes in resistance and reflectivity of thin Pd films deposited on a glass surface and exposed to hydrogen. The films are produced using plasma assisted physical vapor deposition. The resulting films are 15 to 60nm thick. The films are exposed to a mixture of 2% hydrogen gas and 98% nitrogen for five minutes. The changes in resistance and reflecti
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