Optical properties of Pd thin films exposed to hydrogen studied by transmittance and reflectance spectroscopy

Abstract

The optical properties of hydrogen exposed palladium (Pd) and palladium oxide (PdO) thin films are calculated from reflectance and transmittance measurements in the visible and near infrared range (400–900nm). The time evolution of the films’ optical constants when exposed to hydrogen is shown. The real part of palladium’s refractive index increases about 5%, whereas the imaginary part decreases nearly 15% after hydrogen absorption. The Pd films’ resistance also increased upon hydrogen absorption, as expected. Pd oxide reduces to metallic palladium upon hydrogenation, showing a dramatic change in all the properties. The palladium films’ resistance initially decreases after a first exposure to 5Torr of hydrogen, and this is tentatively explained by the reaction of hydrogen with impurities trapped in the films.

Optical sensor for hydrogen gas based on a palladium-coated polymer microresonator

“…We also note that a decrease in sensitivity of the devices was typically observed upon repeated cycles of H 2 exposure. This was attributed to the incomplete removal of hydrogen from the Pd lattice [28] and partial breaking of bonds between the Pd and SU-8 surfaces as discussed in the following paragraphs. For a given sensor device, we always used data recorded during the first set of experiments in calculating the sensitivity values reported in this paper.…”

Plasmonic Hydrogen Sensor at Infrared Wavelengths

“…The observed redshift of the plasmonic peak occurs as a result of changes in these optical constants. (22) Moreover, the hydrogenated Pd feature has appeared on the plasmonic spectral width. Both NDA and MHA spectra were broadened with hydrogenation around 350 nm.…”

Optical readout of hydrogen storage in films of Au and Pd

“…Typically, transmittance increased while reflectance decreased. An optical transmission measurement of a Pd film hydrogenation is sensitive due to the exponential dependence of transmittance, T, on the imaginary part of the refractive index of a strongly absorbing film (Pd with hydrogen)ñ = n + ik on a non-absorbing substrate of refractive index, n s (glass) [12]:…”

“…However, a more sensitive optical detection of Pd hydrogenation can be obtained by transmission measurements [12]. A "switchable mirror" that have a rare metal (Gd or Y) mirror with Pd thin film on top shows a large transmission change in visible wavelength region [13,14].…”