Safe and simple detection of sparse hydrogen by Pd-Au alloy/air based 1D photonic crystal sensor

Abstract

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy.

Three-periodic 1D photonic crystals for designing the photonic optical devices operating in the infrared regime

“…3(a), 3(d), and 3(g)]. However, the widths of the resulting PBGs are larger in comparison to those of the structure (ST) 9 , and the intraband modes appear in the spectra as a result of the presence of the lowoptical-contrast subcells (AZ) 3 . These modes can be treated as the defect modes appeared due to the subcells (AZ) 3 which act as complex defect layers with respect to the single-periodic structure composed of the high-optical-contrast subcells.…”

“…These modes can be treated as the defect modes appeared due to the subcells (AZ) 3 which act as complex defect layers with respect to the single-periodic structure composed of the high-optical-contrast subcells. The number and the positions of the intraband modes can vary with the wavelength 0l of the PBG center of the subcell (AZ) 3 . Indeed, the increase of 0l can shorten the frequency distance between the peaks (see, for instance, Figs.…”

“…6(h)]. Such behavior can be explained by the fact that, in this case, the intraband modes of the structure are due to presence of the subcells (AZ) 3 (as periodic defects) inside the regular structure (ST) 9 which forms the PBG.…”

“…During two last decades, one-dimensional (1D) photonic crystals (PC) have been successfully implemented in various photonic and optoelectronic devices: solar cells, sensors, 3D matrices, fluorescent amplifying devices, color displays, sensors, etc. [1][2][3]. The possibility of the distributed-feedback laser structures fabrication using a 1D PC is currently discussed [4].…”

Distributed Bragg Reflectors Employed in Sensors and Filters Based on Cavity-Mode Spectral-Domain Resonances

“…Most importantly, a direct free-space excitation of BSWs is not possible, contrary to TPs [ 20 ], as states of a 1DPhC within the band gap at the interface between a metal and the 1DPhC exist. This concept, which has been extensively studied and utilized [ 21 , 42 , 43 ], can also be extended to all-dielectric 1DPhC-based sensors employing defects or optical cavities [ 4 , 5 , 6 , 7 , 28 , 29 , 30 , 31 , 32 , 33 , 44 ], characterized by a strong confinement of light in the resonant cavity, which is manifested by very narrow resonances at the normal incidence of light both in transmission and reflection. These resonances exist within the wavelength range of the band gap and correspond to localized modes in the defect, for which its introduction in 1DPhC permits defect states.…”