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In-situ determination of the complex permittivity of ultrathin H2-infused palladium coatings for plasmonic fiber optic sensors in the near infrared

Abstract

In situ and continuous monitoring of hydrogen concentration is a key to evaluate the operation mechanism and efficiency of hydrogen based green energy devices. However this task remains challenging. For example, the present methods are not capable of providing the complex permittivity of hydrogen sensitive material as a function of hydrogen concentration thereby enabling the design and fabrication of sensing devices that do not require individual calibration prior to use. In this paper, we report measurements of the complex permittivity of 7 nm thick palladium thin films exposed to concentrations of 0 to 3 % (by volume) of hydrogen in nitrogen at wavelengths near 1310 nm. Measurements were carried out with a tilted fiber Bragg grating first coated with 30 nm of gold and then palladium at several thicknesses between 3 and 43 nm. The tilt angle of the grating was fixed at 23 degrees in order to allow the excitation of surface plasmon resonances on the gold surface by high order cladding modes in air at wavelengths near 1310nm. Simulations of the grating response based on measurable experimental parameters indicated that for palladium thicknesses between 3 and 10 nm the measured changes in the grating transmission become independent of thickness. Therefore for a 7 nm thick film any change in transmission can be traced directly to changes in permittivity. The relative change of the permittivity of the palladium layer was found to scale linearly with hydrogen concentration with a scaling factor of -0.15/%H2 for hydrogen concentrations between 0 and 1.7%. The limit of detection of the grating configuration used was determined to be 380 ppm at three times the standard deviation for measurements averaged over 80 seconds. Using standard fiber optic instrumentations and single mode fiber, the signal to noise ratio was over 100.

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Publication details

The article was received on 16 Mar 2018, accepted on 12 Apr 2018 and first published on 12 Apr 2018


Article type: Paper
DOI: 10.1039/C8TC01278D
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    In-situ determination of the complex permittivity of ultrathin H2-infused palladium coatings for plasmonic fiber optic sensors in the near infrared

    X. Zhang, S. Cai, F. Liu, H. Chen, P. Yan, Y. Yuan, T. Guo and J. Albert, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC01278D

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