Hydrogen sensing via anomalous optical absorption of palladium-based metamaterials

Molecular Plasmonics with Metamaterials

Molecular plasmonics, the area which deals with the interactions between surface plasmons and molecules, has received enormous interest in fundamental research and found numerous technological applications. Plasmonic metamaterials, which offer rich opportunities to control the light intensity, field polarization, and local density of electromagnetic states on subwavelength scales, provide a versatile platform to enhance and tune light-molecule interactions. A variety of applications, including spontaneous emission enhancement, optical modulation, optical sensing, and photoactuated nanochemistry, have been reported by exploiting molecular interactions with plasmonic metamaterials. In this paper, we provide a comprehensive overview of the developments of molecular plasmonics with metamaterials. After a brief introduction to the optical properties of plasmonic metamaterials and relevant fabrication approaches, we discuss light-molecule interactions in plasmonic metamaterials in both weak and strong coupling regimes. We then highlight the exploitation of molecules in metamaterials for applications ranging from emission control and optical modulation to optical sensing. The role of hot carriers generated in metamaterials for nanochemistry is also discussed. Perspectives on the future development of molecular plasmonics with metamaterials conclude the review. The use of molecules in combination with designer metamaterials provides a rich playground both to actively control metamaterials using molecular interactions and, in turn, to use metamaterials to control molecular processes.

Tunable Plasmonic Resonance Sensor Using a Metamaterial Film in a D-Shaped Photonic Crystal Fiber for Refractive Index Measurements

Subwavelength cells of metallic nanorods arrayed in a dielectric background, termed “metamaterials”, present bulk properties that are useful to control and manipulate surface plasmon resonances. Such feature finds tremendous potential in providing a broad manifold of applications for plasmonic optical sensors. In this paper, we propose a surface-plasmon-resonance-based sensor with spectral response tunable by the volume fraction of silver present in a metamaterial layer deposited on a D-shaped photonic crystal fiber. Using computational simulations, we show that sensitivity and resolution can be hugely altered by changing the amount of constituents in the metamaterial, with no further modifications in the structure of the sensor. Moreover, the designed sensor can also be applied to label the average volume fraction of silver in the metamaterial layer and then to estimate its effective constitutive parameters.

Inter-Cavity Coupling Strength Control in Metal/Insulator Multilayers for Hydrogen Sensing

Hydrogen (H2) sensing is crucial for modern energy storage technology, which looks to hydrogen as the most promising alternative to fossil fuels. In this respect, magnesium (Mg) offers unique possibilities, since magnesium and hydrogen easily undergo a reversible hydrogenation reaction where Mg reversibly converts into MgH2. From an optical point of view, this process produces an abrupt refractive index change, which can be exploited for sensing applications. To maximize this opportunity, we envision an architecture composed of two Ag/ITO/Mg metal/dielectric resonators facing each other and displaced by 200 nm of vacuum. This structure forms a so-called Epsilon-Near-Zero (ENZ) multi-cavity resonator, in which the two internal Mg layers, used as tunneling coupling metals, are accessible to environmental agents. We demonstrate that the hydrogenation of the two Mg layers leads to substantial changes in the strong coupling between the cavities composing the entire resonator, with a consequent abrupt modification of the spectral response, thus enabling the sensing mechanism. One of the main advantages of the proposed system with respect to previous research is that the proposed multilayered architecture avoids the need for lithographic processes. This feature makes the proposed architecture inexpensive and wafer-to-chip scalable, considering that each kind of substrate from common glass to silicon can be used. Therefore, our sensing architecture offers great promise for applications in embedded H2 sensors.

CMOS-compatible plasmonic hydrogen sensors with a detection limit of 40 ppm

Sensing of leakage at an early stage is crucial for the safe utilization of hydrogen. Optical hydrogen sensors eliminate the potential hazard of ignition caused by electrical sparks but achieve a detection limit far higher than their electrical counterparts so far. To essentially improve the performance of optical hydrogen sensors in terms of detection limit, we demonstrate in this work a plasmonic hydrogen sensor based on aluminum-palladium (Al-Pd) hybrid nanorods. Arranged into high-density regular arrays, the hybrid nanorods are capable of sensing hydrogen at a concentration down to 40 ppm, i.e., one thousandth of the lower flammability limit of hydrogen in air. Different sensing behaviors are found for two sensor configurations, where Pd-Al nanorods provide larger spectral shift and Al-Pd ones exhibit shorter response time. In addition, the plasmonic hydrogen sensors here utilize exclusively CMOS-compatible materials, holding the potential for real-world, large-scale applications.

New Trends in the Simulation of Nanosplasmonic Optical D-Type Fiber Sensors

This article presents a review of the numerical techniques employed in simulating plasmonic optical sensors based on metal-dielectric nanostructures, including examples, ranging from conventional D-type fiber sensors, to those based on photonic crystal D-type fibers and incorporating metamaterials, nanowires, among other new materials and components, results and applications. We start from the fundamental physical processes, such as optical and plasmonic mode coupling, and discuss the implementation of the numerical model, optical response customization and their impact in sensor performance. Finally, we examine future perspectives.

High-resolution, flexible, and transparent nanopore thin film sensor enabled by cascaded Fabry-Perot effect

This Letter reports a method to significantly improve the optical resolution of the anodic aluminum oxide (AAO) nanopore thin film sensor based on multi-cavity Fabry-Perot interference. The newly designed sensor is fabricated by bonding a layer of transparent polymer thin film (pTF), which is polydimethylsiloxane (PDMS), to a transparent AAO thin film to form a flexible pTF-nanopore sensor. In comparison with the AAO nanopore thin film sensor, the pTF-nanopore sensor shows a much-improved quality (Q) factor and optical resolution. Typical thicknesses of a PDMS layer and an AAO layer of the pTF-nanopore sensor are 80 μm and 2 μm, respectively. The pTF-nanopore sensor used for angle detection shows a sensitivity of 0.4 nm/deg with a resolution of 0.2 deg. The pTF-nanopore sensor can also be used for temperature monitoring with a sensitivity of 0.2 nm/°C and a resolution of 1°C.