Ultrahigh Figure Of Merit Research Articles

Optical fiber sensor based on magneto-optical surface plasmon resonance with ultra-high figure of merit

Compared to surface plasmon resonance (SPR), the sensors based on the magneto-optical SPR (MOSPR) technique have much higher figure-of-merit (FOM). However, there are no reports about applying MOSPR in the optical fiber structure now. In this work, a novel D-shaped optical fiber sensor based on the MOSPR technique is proposed. The D-shaped optical fiber is coated with a thin silver film and a magneto-optical (MO) material film of Cerium-doped Yttrium-Iron garnet (CeYIG). By applying a magnetic field on the sensing region, the magneto-optical Kerr effect (MOKE) of the CeYIG layer and the related MOSPR phenomenon could be excited when appropriate light is transmitted in the proposed optical fiber sensor. The influence of the structural parameters including the residual cladding thickness, silver and MO material film thicknesses are analyzed theoretically by the finite element method (FEM). With the optimal parameters, the sensor achieves the sensitivity of 5304 nm RIU−1. Since the peak width of MOSPR spectra is much narrower than that of the SPR spectra, the FOM of the sensor is largely enhanced to 3864 RIU−1 on average and 13260 RIU−1 in maximum, which surpasses the optical fiber SPR sensors vastly. The miniaturized and simple design of the D-shaped optical fiber MOSPR sensor, coupled with the ultra-high FOM, offers itself great potential in biochemical sensing applications.

Exploiting Thin-Film Properties and Guided-Mode Resonance for Designing Ultrahigh-Figure-of-Merit Refractive Index Sensors

Guided-mode resonance (GMR) gratings have emerged as a promising sensing technology, with a growing number of applications in diverse fields. This study aimed to identify the optimal design parameters of a simple-to-fabricate and high-performance one-dimensional GMR grating. The structural parameters of the GMR grating were optimized, and a high-refractive-index thin film was simulated on the grating surface, resulting in efficient confinement of the electric field energy within the waveguide. Numerical simulations demonstrated that the optimized GMR grating exhibited remarkable sensitivity (252 nm/RIU) and an extremely narrow full width at half maximum (2 × 10−4 nm), resulting in an ultra-high figure of merit (839,666) at an incident angle of 50°. This performance is several orders of magnitude higher than that of conventional GMR sensors. To broaden the scope of the study and to make it more relevant to practical applications, simulations were also conducted at incident angles of 60° and 70°. This holistic approach sought to develop a comprehensive understanding of the performance of the GMR-based sensor under diverse operational conditions.

Flexible, Transparent and Conductive Metal Mesh Films with Ultra-High FoM for Stretchable Heating and Electromagnetic Interference Shielding.

Despite the growing demand for transparent conductive films in smart and wearable electronics for electromagnetic interference (EMI) shielding, achieving a flexible EMI shielding film, while maintaining a high transmittance remains a significant challenge. Herein, a flexible, transparent, and conductive copper (Cu) metal mesh film for EMI shielding is fabricated by self-forming crackle template method and electroplating technique. The Cu mesh film shows an ultra-low sheet resistance (0.18 Ω □-1), high transmittance (85.8%@550nm), and ultra-high figure of merit (> 13,000). It also has satisfactory stretchability and mechanical stability, with a resistance increases of only 1.3% after 1,000 bending cycles. As a stretchable heater (ε > 30%), the saturation temperature of the film can reach over 110°C within 60s at 1.00V applied voltage. Moreover, the metal mesh film exhibits outstanding average EMI shielding effectiveness of 40.4dB in the X-band at the thickness of 2.5μm. As a demonstration, it is used as a transparent window for shielding the wireless communication electromagnetic waves. Therefore, the flexible and transparent conductive Cu mesh film proposed in this work provides a promising candidate for the next-generation EMI shielding applications.

Achieving Superior Thermoelectric Performance in Ge4Se3Te via Symmetry Manipulation with I–V–VI2 Alloying

AbstractAlthough orthorhombic GeSe is predicted to have an ultrahigh figure of merit, ZT ≈ 2.5, up to now, the highest experimental value is ≈0.2 due to the low carrier concentration (nH ≈ 1018 cm−3). Improving symmetry is an effective approach for enhancing the ZT of GeSe‐based materials. With Te‐alloying, Ge4Se3Te displays the two‐dimensional hexagonal structure and high nH ≈ 1.23 × 1021 cm−3. Interestingly, Ge4Se3Te transformed from the hexagonal into the rhombohedral phase with only ≈2% I–V–VI2‐alloying (I = Li, Na, K, Cu, Ag; V = Sb, Bi; VI = Se, Te). According to the calculated results of Ge0.82Ag0.09Bi0.09Se0.614Te0.386 single‐crystal grown via AgBiTe2‐alloying, it exhibits a higher valley degeneracy than the hexagonal Ge4Se3Te. For instance, AgBiTe2‐alloying induces a strong band convergence and band inversion effect, resulting in a significantly enhanced Seebeck coefficient and power factor with a similar nH from 17 µV K−1 and 0.63 µW cm−1 K−2 for pristine Ge4Se3Te to 124 µV K−1 and 5.97 µW cm−1 K−2 for 12%AgBiTe2‐alloyed sample, respectively. Moreover, the sharply reduced phonon velocity, nano‐domain wall structure, and strong anharmonicity lead to low lattice thermal conductivity. As a result, a record‐high average ZT ≈0.95 over 323–773 K with an excellent ZT ≈ 1.30 is achieved at 723 K.

All-inorganic flexible epitaxial SrNbO3/mica thin films with ultrahigh figure of merit as indium-free transparent conductors

Nowadays, flexible transparent conductors (TCs) have been widely applied for solar cells, stretchable integrated circuits, sensor networks, and human-machine interaction devices. Recently, nondoped correlated metallic oxides (CMOs) have aroused great interest as indium-free TCs. In this work, an all-inorganic flexible CMO thin film with an ultrahigh figure of merit (FOM) value was fabricated using a simple preparation technology: the direct deposition of epitaxial SrNbO3 thin films on a stratiform mica substrate via a pulsed laser deposition (PLD) process. From the measured optical transmittance (Tr) spectra in conjunction with the ellipsometic data, it is found that SrNbO3 film possesses a superior visible light transparency compared with commonly investigated SrVO3 due to its larger bandgap. The charge transport measurements indicate that the dc electrical conductivity (σ) of SrNbO3 is higher than that of SrVO3, attributed presumably to a weaker electron correlation and therefore a smaller effective electron mass (m*) in SrNbO3. Bending cyclic tests reveals high mechanical durability and bending stability in SrNbO3 films. This detailed investigation demonstrates a great potential of the all-inorganic flexible epitaxial SrNbO3/mica film as an indium-free TC with high performance for future optoelectronic applications.

Perovskite nanowires-based graphene plasmonic waveguides with low loss and low gain threshold

We designed a perovskite nanowire-based graphene plasmonic waveguide, where the perovskite nanowire is located on the graphene-insulator-metal (GIM) platform. The finite element method is employed to investigate the impact of the perovskite nanowire radius, graphene layer thickness, Fermi energy level of the graphene, thickness of the low index dielectric layer, and permittivity of dielectric layer on the mode properties. The results indicate that the hybrid mode exhibits very low propagating loss and ultra-high figure of merit. Besides, when the radius of the perovskite nanowire exceeds 200 nm, an ultra-low gain threshold below 0.1 μm−1 could be achieved. Our findings could have potential applications in plasmonic waveguide-based devices, such as lasers, modulators, sensors, etc.

Ultrasensitive Refractive Index Sensing Based on Hybrid High-Q Metasurfaces

High sensitivity and a large quality factor (Q) are two desirable goals to achieve a high figure of merit (FoM) in refractive index (RI) sensing. However, simultaneously satisfying these two goals is challenging. Herein, we propose a new class of hybrid high-Q metasurfaces, which are dielectric arrays standing on a Au plasmonic nanofilm, possessing the advantages of both high RI sensitivity and a large Q. The hybrid metasurface can support the plasmon-coupled lattice mode, which has extremely narrow full width at half-maximum (fwhm) resulting in a high-Q. The hybrid metasurface can be fabricated by a facile straightforward lithography technique and exhibits ultrahigh FoM values over a wide RI range (1–1.384) due to its narrow fwhm (smaller than 1 nm) and tunable high RI sensitivity. The highest Q and FoM values of 2370 and 1431 were experimentally demonstrated, respectively, giving the proposed hybrid metasurface great potential for building advanced optical biosensors in future applications.

All-dielectric metasurface-based multimode sensing with symmetry-protected and accidental bound states in the continuum

Symmetry-protected and accidental bound states in the continuum (BICs) are generated by various triggering mechanisms, and it is challenging to use them together for sensing. This study designed an all-dielectric metasurface that produced BICs in the terahertz band. Moreover, we investigated eight mode distributions by energy band analysis, of which four modes had symmetry-protected BICs at the high-symmetry Γ point, and three had accidental BICs at the non-Γ point, all with quality factors up to 109. Using multipole analysis and parameter adjustment, we investigated the contribution of multipole moments to the far field, the electromagnetically induced transparency caused by the intermodal coupling, and the merging of accidental BICs. Finally, we used six BICs for multimode sensing, where the figure of merit (FOM) of the symmetry-protected BICs reached 108, and the FOM of the accidental BICs reached 105, providing a new perspective on terahertz linear sensor devices. These findings will open a new avenue for the study of terahertz multimode sensors with ultra-high FOM.

High-sensitive and millisecond-response all-nanofiber-optic humidity sensor using evanescent coupling

The reported humidity sensors usually rely on various sensitive materials to increase the humidity sensitivity, while leading to long response time (1 s ∼10 s). By now, it is still challenging to obtain both high-sensitivity and ultrafast-response (∼tens of ms), i.e., high figure of merit (FOM), for optical humidity sensors. Here, we demonstrate an all-nanofiber-optic strategy to break the limit by using evanescent coupling between a nanofiber (NF) and a substrate without any extra sensitive materials. To implement the sensor, a NF is suspended over a 450 nm deep pit etched in a glass-slide. With increase in the ambient humidity, a thin water film over the NF is formed and strengthens both the evanescent field outside the NF and evanescent coupling into the pit, thus leading to decrease in the transmission of the NF. Experiment shows that the sensor achieved a high sensitivity of − 1.162 dB/%RH in the high RH range of 66.5–83.8%RH with ultrafast response (40 ms) and recovery (100 ms) times. A sensor FOMs, defined as the absolute ratio of sensitivity to response time or recovery time, are also proposed to assess the comprehensive performance of the sensor. The response and recovery FOM of the demonstrated sensor here are up to 29.05 |(dB/%RH)/s| and 11.62 |(dB/%RH)/s|, respectively, which are 2–3 order of magnitude higher than the sensor reported previously. Interestingly, the NF sensor also exhibits a high RH resolution of 0.0189%RH in our experiment. The ultra-high FOMs and flexibility of the sensor allows to easily be integrated with a mask for continuously human fast breath monitoring with a 10 Hz bandwidth. Moreover, our sensor has potential applications in the non-contact switch, noninvasive diagnostic of skin conditions and micron location sensing. The proposed sensing mechanism could provide a novel all-fiber-optic strategy to improve both RH sensitivity and response of the optic humidity sensor simultaneously.

Electromagnetic multipolar quasi-bound states in the continuum for optical sensing

Optical sensing is of vital importance in many applications, which has received extensive attention in recent years. The pursuit of optical sensing mechanism with higher figure of merit (FOM) is very important for various sensing applications. Bound states in the continuum (BIC) with theoretical infinite Q factor is an ideal candidate to effectively improve the FOM of optical sensor. Herein, we propose and numerically demonstrate an optical refractive index sensor based on the electromagnetic multipolar quasi-BICs of all-dielectric metasurfaces. Based on the eigen-solution and excitation simulation, we find that magnetic dipole (MD) quasi-BIC is the best candidate for optical refractive index sensing among the electromagnetic multipolar quasi-BICs in the proposed all dielectric metasurface. The sensitivity (S) and the value of FOM for the optical refractive index sensor are 225.27 nm/RIU and 441762.93, respectively. It is anticipated that our results might shed new light on the optical refractive index sensing of high sensitivity and ultra-high FOM.

Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba0.6Sr0.4TiO3 (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y3Fe5O12 (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y3Fe5O12/Ba0.6Sr0.4TiO3 (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.

Fiber optics - A new route to surface wave sensors with ultra-wide refractive index sensing range and ultra-high figure of merit

Fiber optics - A new route to surface wave sensors with ultra-wide refractive index sensing range and ultra-high figure of merit

All-Dielectric Metasurface Based on Complementary Split-Ring Resonators for Refractive Index Sensing

Thanks to their lower losses and sharper resonances compared to their metallic counterparts, all-dielectric metasurfaces are attracting a quickly growing research interest. The application of such metasurfaces in the field of refractive index sensing is extremely attractive, especially due to the expected high performance and the simplicity of the sensing element excitation and readout. Herein, we report on an all-dielectric silicon metasurface based on complementary split-ring resonators (CSRRs) optimized for refractive index sensing. A quasi-bound state in the continuum (quasi-BIC) with an ultra-high quality factor can be excited in the near-infrared (NIR) window by violating the structure symmetry. By using the three-dimensional finite element method (3D-FEM), a refractive index sensor for biomedical applications with an ultra-high figure of merit (FoM > 100,000 RIU−1) has been designed, exploiting the quasi-BIC resonance. The proposed design strategy opens new avenues for developing flat biochemical sensors that are accurate and responsive in real time.

Defect Engineering Boosted Ultrahigh Thermoelectric Power Conversion Efficiency in Polycrystalline SnSe.

Two-dimensional (2D)-layered atomic arrangement with ultralow lattice thermal conductivity and ultrahigh figure of merit in single-crystalline SnSe drew significant attention among all thermoelectric materials. However, the processing of polycrystalline SnSe with equivalent thermoelectric performance as single-crystal SnSe will have great technological significance. Herein, we demonstrate a high zT of 2.4 at 800 K through the optimization of intrinsic defects in polycrystalline SnSe via controlled alpha irradiation. Through a detailed theoretical calculation of defect formation energies and lattice dynamic phonon dispersion studies, we demonstrate that the presence of intrinsically charged Sn vacancies can enhance the power factor and distort the lattice thermal conductivity by phonon-defect scattering. Supporting our theoretical calculations, the experimental enhancement in the electrical conductivity leads to a massive power factor of 0.9 mW/mK2 and an ultralow lattice thermal conductivity of 0.22 W/mK through the vacancy-phonon scattering effect on polycrystalline SnSe. The strategy of intrinsic defect engineering of polycrystalline thermoelectric materials can increase the practical implementation of low-cost and high-performance thermoelectric generators.

Topological hybrid nanocavity for coupling phase transition

Topological photonic nanocavity provides a robust platform for realizing nano-photonic devices and studying light–matter interaction. Here, a topological photonic-plasmonic hybrid nanocavity, assembling a topological photonic crystal (PhC) nanocavity with a plasmonic nano-antenna, is proposed to have an ultra-high figure of merit Q/V of , which is two orders higher than that of the bare topological PhC nanocavity. The single-atom cooperativity parameter is improved by over 60 times due to the large enhancement of Q/V, which makes the coupling between light and a single emitter enter a strong coupling region in topological photonic realm for the first time. Meanwhile, strong coupling and weak coupling can be easily switched in the topological hybrid system by tuning the structure dimension of plasmonic nano-antennas. This work provides a robust platform to control coupling phase transition between light and a single emitter, which has great potential in topological lasers, quantum optics and quantum information.

Ultrahigh Thermoelectric Performance in Environmentally Friendly SnTe Achieved through Stress‐Induced Lotus‐Seedpod‐Like Grain Boundaries

AbstractIn an effort to improve the thermoelectric performance of the environmentally friendly SnTe, here, a multilevel structure composed of “lotus‐seedpod‐like” grain boundaries, dense dislocations, and nanopores is innovatively constructed, which synergistically reduces the sound velocity and the phonon relaxation time, resulting in ultralow lattice thermal conductivity throughout a wide temperature range. An ultrahigh figure of merit, ZT, of ≈1.7 and an unprecedented average ZT of ≈1 from 300 to 873 K are obtained. In contrast to the common pore‐forming method of volatilization, the strategy of stress‐induced recrystallization and gas expansion cogenerating interfacial pores that is used here, is believed to be more widely applicable for many other materials, which opens up a new avenue for improving thermoelectric performance.

Electromagnetic-Induced Transparency Resonance with Ultrahigh Figure of Merit Using Terahertz Metasurfaces

In this paper, a terahertz metasurface supercell consists of two ring resonators with slightly different radii is proposed. Electromagnetic-induced transparency (EIT)–like resonance is excited with an ultrahigh figure of merit. Furthermore, the impact of the coupling between the two rings is investigated on the transmission amplitude response, the quality factor, and the EIT peak amplitude by varying the radius of the top resonator. The achieved figure of merit of the EIT peak reaches 88.65 and almost 20,000 when gold and a perfect electric conductor are used for the metallic layer, respectively. The simplicity and unique properties of the proposed design could render it to be a desirable candidate for filtering, slow light applications, and sensing.

One-Dimensional Photonic Crystal Inner Coated Hollow Fiber Sensor Based on Bloch Surface Wave With Ultra-High Figure of Merit

A high-performance Bloch surface wave (BSW) sensor based on the hollow fiber (HF) inner coated with the one-dimensional photonic crystal (1DPC) consisting of TiO2 and SiO2 bilayers is proposed. Performances including sensitivity and figure of merit (FOM) of the sensor are investigated theoretically with the ray transmission model. Several structure parameters such as the center wavelength of 1DPC, the thickness of the cap layer and the bilayer period are optimized to obtain a best performance of the sensor. The results show that the proposed sensor has an ultra-high FOM over 1100 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , which is approximately two and one orders of magnitude higher than that of the HF surface plasmon resonance (SPR) sensor and HF long-range SPR sensor, respectively. Moreover, the proposed sensor has a much broader practical RI detection range, which makes it more useful in sensing applications. The performance of the proposed sensor applicated in temperature sensing is also estimated to prove its application potential.

Hybridization-induced resonances with high-quality factor in a plasmonic chipscale ring-disk nanocavity

ABSTRACT Plasmonic resonators have drawn more attention due to the ability to confine light into subwavelength scale. However, they always suffer from a low-quality (Q) factor owing to the intrinsic loss of metal. Here, we numerically propose a plasmonic resonator with ultra-high Q factor based on plasmonic metal–insulator-metal (MIM) waveguide structures. The resonator consists of a disk cavity surrounded by a concentric ring cavity, possessing an ultra-small volume. Arising from the plasmon hybridization between plasmon modes in the disk and ring cavity, the induced bonding hybridized modes have an ultra-narrow full width at half maximum (FWHM) as well as ultra-high Q factors. The FWHM can be nearly 1 nm and Q factor can be more than 400. Furthermore, such a device can act as a refractive index sensor with an ultra-high figure of merit (FOM). This work provides a novel approach to design plasmonic high-Q-factor resonators and has potential on-chip applications such as filters, multi-spectral sensors and nanolasers.

Bound-state in the continuum of a photonic crystal metasurface: a platform for ultrasensitive sensing and near field amplification

The localization of the electromagnetic field at the nanoscale can play a key role in many applications, such as sensing, spectroscopy and energy conversion. In the last years, great efforts have been performed to study and realize all-dielectric loss-free nanostructures to confine the radiation without the limits imposed by the plasmonic systems. Here we demonstrate that the field enhancement in proximity of a photonic crystal metasurface supporting bound states in the continuum can be explored to boost the light-matter interaction. We design and realize an innovative sensing scheme for bulk and surface measurement with ultra-high figure of merit and apply this new configuration for studying a specific protein-protein interaction. The recognition scheme can be coupled to a fluorescence-based sensing approach, which exploits the capability of the sensor to strongly enhance fluorescence signals. Our results provide new solutions for light manipulation at the nanoscale, especially for sensing and nonlinear optics applications.