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Modelling of measured optical properties of Pd–Au alloy ultrathin film for room temperature hydrogen sensing
Author(s) -
Mitra Sanchali,
Chattopadhyay Rik,
Ghosh Jiten,
Bysakh Sandip,
Bhadra Shyamal K.
Publication year - 2016
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201600051
Subject(s) - materials science , alloy , hydrogen , thin film , substrate (aquarium) , dielectric , fermi level , analytical chemistry (journal) , optics , optoelectronics , nanotechnology , composite material , chemistry , oceanography , physics , organic chemistry , chromatography , quantum mechanics , geology , electron
A theoretical framework is presented to describe optical properties of palladium gold alloy ultra‐thin film of thickness about 5 nm. Density functional theory is employed to calculate complex dielectric function of hydrogen loaded Pd 3 Au alloy. Using Bruggeman's effective medium theory, the effective dielectric function of hydrogenated alloy is calculated in case of non‐uniform diffusion of hydrogen starting from very low concentration. Reflectance of deposited film on silica substrate is calculated using transfer matrix method and results are compared with the measured reflectance of sputter deposited thin film of alloy on identical substrate. The change of reflectance with hydrogen concentration is also calculated and verified experimentally. In both the cases, hydrogen loaded films show low reflectance due to reduction of the available electronic states near Fermi level compared to unloaded films. From TEM images and Grazing Incidence X‐ray diffraction analyses, crystal structure of the deposited alloy film is predicted. Using this alloy a four‐layered plasmonic waveguide is designed for room temperature hydrogen sensing. Analytical calculations show that absorption loss of fundamental TM mode of the waveguide at 633 nm changes almost linearly with hydrogen concentration variation. The loss will decrease about 5 dB/100% atomic concentration of hydrogen for 10 µm device length.