Optical and electrical properties of hydrided palladium thin films studied by an inversion approach from transmittance measurements

Vargas, William E.; Rojas, I.; Azofeifa, D. E.; Clark, N.J.

doi:10.1016/j.tsf.2005.08.346

Cited by 72 publications

(51 citation statements)

References 24 publications

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“…Here we ignore the volume expansion resulting from lattice constant increase [23]. In order to examine the difference in reflectance the transformation to PdH x makes, we obtained dielectric function values of Pd and PdH x reported by Vargas et al [24] for 0.82 hydrogen concentration, and computed the absorptive characteristics of 3-layer MIM system for normal incidence where P dH x is in β-phase x 0.82 [4]. It should also be noted that both the real and imaginary parts of the refractive index decreases with increasing H 2 concentration, and thus the results should be adjusted accordingly.…”

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Perfectly absorbing ultra thin interference coatings for hydrogen sensing

et al. 2016

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Here we numerically demonstrate a straightforward method for optical detection of hydrogen gas by means of absorption reduction and colorimetric indication. A perfectly absorbing metal-insulator-metal (MIM) thin film interference structure is constructed using a silver metal back reflector, silicon dioxide insulator, and palladium as the upper metal layer and hydrogen catalyst. The thickness of silicon dioxide allows the maximizing of the electric field intensity at the Air∕SiO 2 interface at the quarter wavelengths and enabling perfect absorption with the help of highly absorptive palladium thin film ∼7 nm. While the exposure of the MIM structure to H 2 moderately increases reflection, the relative intensity contrast due to formation of metal hydride is extensive. By modifying the insulator film thickness and hence the spectral absorption, the color is tuned and eyevisible results are obtained. Hydrogen H 2 sensing requires development of highly sensitive, reliable, and short response-time sensors due to its use in critical applications such as fuel-cells, pharmaceuticals, and petroleum and chemical production. Palladium (Pd) can absorb H 2 upon exposure and transform into palladium hydride PdH x , and the optical and electrical properties of Pd metal are changed by such transformation [1]. Recent advancements in plasmonic research and nanofabrication techniques led the development of surface and localized surface plasmon-based (LSPR) hydrogen sensors using Pd [2][3][4]. Nanoparticle or LSPR sensors show good potential for faster response times [5,6]. However, the broad spectral response of LSPR-based hydrogen sensors arises as an issue, which, later on, led the researchers to reduce the linewidth with the help of a whispering gallery mode cavity [7], and to develop highly sensitive hybrid sensors such as using Pd with a good plasmonic metal [8,9]. For example, Alivisatos and co-workers have demonstrated highly sensitive hydrogen sensors by placing Pd nanoparticles close to the sharp corners of nanoantennas [10].Such sensing mechanisms are based on probing of the scattering properties of nanoantenna-Pd nanoparticle structure, rather than the direct probing of scattering properties of Pd nanoparticles that shows small wavelength shifts upon hydrogen exposure. Other important plasmon-based hydrogen sensing mechanism is based on plasmonic-perfect absorbers [11][12][13], and single crystal Pd and its alloy-coated nanowires [14,15]. The motivation behind the absorbance-based sensors is to minimize the requirement for the bulky optical setups, expensive light sources, and spectrometers by only probing the scattered light intensity at perfect-absorption wavelength. Moreover, some of the recent studies report the visual detection of hydrogen by using thin film optical coatings to circumvent the problems of hydrogen sensors based on electrical readout [16,17]. Despite the demonstration of visual detection of H 2 , the thin film structure did not take full advantage of the lossy nature of Pd films. In this study, we demo...

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Perfectly absorbing ultra thin interference coatings for hydrogen sensing

et al. 2016

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“…We conclude that the difference between the real and imaginary part of the dielectric permittivity upon hydrogenation is the cause of the wavelength dependence of the sensor response. Vargas et al 10 point out that the variations in the real and the imaginary part of the Pd dielectric permittivity upon Hydrogen absorption is influenced by the nature of the substrate: conducting or no-conducting. Henceforth, we expect a different sensitivity when a conducting sticking layer will be used between the Pd layer and the fiber core.…”

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confidence: 99%

A distributed optical fiber sensor for hydrogen detection based on Pd, and Mg alloys

et al. 2010

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Abstract:An optical fiber containing structured hydrogen sensing points, consisting of Palladium and/or Magnesium alloys is proposed and characterized. The sensitive layer is deposited on the outside of a multimode fiber, after removing the optical cladding. The sensor is based on a measurement technique which uses the Surface Plasmon Resonance effect. Compared to previous work 1 which was performed at a single wavelength of 670nm, this study was done in the range of 450 to 900nm. A continuous change in intensity is observed as a function of the hydrogen concentration between 0.5% and 4% H 2 in Ar. The response shows that the intensity transmitted can either decrease or increase, depending on the selected wavelength. The response time and the reproducibility of the detectors are also discussed. From our experiments and optical simulations we conclude that Pd covered indicator layers based on Mg alloys, such as Mg-Ti, would be even more advantageous compare to Pd layers thanks to their lower hydrogen equilibrium pressures. We will demonstrate an extended sensitivity range by juxtaposing different materials over a fiber section, having different hydrogen equilibrium pressures.

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“…The retrieving procedure was done applying an optimization method based on a projected gradient formalism. The details of this numerical approach have been published elsewhere [10][11][12]. The optimization gradient methods require an initial estimation of the optical constants of the bilayer component materials.…”

Section: From Optical Measurementsmentioning

confidence: 99%