High Figure Of Merit Research Articles

A2LiGaI6 (A = Cs, Rb): New lead-free and direct bandgap halide double perovskites for IR application

Recently, all inorganic double perovskites have drawn a lot of interest as promising solar materials. The optical, structural, thermoelectric, electronic, and mechanical properties of double halide perovskites A2LiGaI6 (A = Cs, Rb) are explored via first-principles calculations with the WIEN2k code, using GGA PBEsol and TB-mBJ potentials. The majority of perovskite materials utilized in the highest-performing solar cells have bandgaps ranging between 1.48 and 1.62 eV. The compounds A2LiGaI6 (A = Cs, Rb) have a direct bandgap of 1.51 eV and 1.55 eV, respectively, and are expected to be useful in solar cells. The optical study shows that there are large absorption bands in the visible region, as determined by the dielectric constant, absorption, and other dependent factors. Their potential for use in solar cells is increased by their absorption in the visible part. The BoltzTraP code has been used to perform thermoelectric studies to assess the electrical, thermal conductivities, and Seebeck coefficient. They are important for construction of thermoelectric generators that harvest heat energy because of their high figure of merit and incredibly low thermal conductivity of lattice at ambient temperature. Furthermore, by examining the spectroscopic limit maximum efficiency, up to 30 % efficiency is predicted for both compositions, which paves the way for the applicability of them in solar energy conversion.

On-body non-invasive glucose monitoring sensor based on high figure of merit (FoM) surface plasmonic microwave resonator

High-figure of merit (FoM) plasmonic microwave resonator is researched as a non-invasive on-body sensor to monitor the human body's blood glucose variation rate in adults for biomedical applications, e.g., diabetic patients. The resonance frequencies of the proposed sensor are measured to be around {f}_{01}=3.25 GHz and {f}_{01}=4.67 GHz over the frequency band of DC to 6GHz which are suitable for monitoring interstitial fluid (ISF) changing rate. The 40times 40 {mathrm{mm}}^{2} sensor is experimentally wrapped on the human body arm to monitor the blood glucose changing rate via amplitude and frequency variations of the sensor. Amplitude variation and frequency shift are measured to be around 7 dB and 30 MHz, respectively. The measured results demonstrate the high precision of the proposed approach to depict a valid diagram for glucose changing rate due to good impedance matching of the designed microwave sensor and human body. The sensor is shown to enhance the sensitivity by a factor of 5 compared to the conventional ones.

Customizable Metal Micromesh Electrode Enabling Flexible Transparent Zn-Ion Hybrid Supercapacitors with High Energy Density.

Emerging flexible and wearable electronic products are placing a compelling demand on lightweight transparent energy storage devices. Owing to their distinguishing features of safety, high specific energy, cycling stability, and rapid charge/discharge advantages, Zn-ion hybrid supercapacitors are a current topic of discussion. However, the trade-off for optical transmittance and energy density remains a great challenge. Here, a high-performance Zn-ion hybrid supercapacitor based on the customizable ultrathin (5µm), ultralight (0.45mg cm-2), and ultra-transparent (87.6%) Ni micromesh based cathode and Zn micromesh anode with the highest figure of merit (84843) is proposed. The developed flexible transparent Zn-ion hybrid supercapacitors reveal excellent cycle stability (no decline after 20000 cycles), high areal energy density (31.69 µWh cm-2), and high power density (512 µW cm-2). In addition, the assembled solid flexible and transparent Zn-ion hybrid supercapacitor with polyacrylamide gel electrolyte shows extraordinary mechanical properties even under extreme bending and twisting operation. Furthermore, the full device displays a high optical transmittance over 55.04% and can be conformally integrated with diverse devices as a flexible transparent power supply. The fabrication technology offers seamless compatibility with industrial manufacturing, making it an ideal model for the advancement of portable and wearable devices.

Side-polished photonic crystal fiber sensor with ultra-high figure of merit based on Bloch-like surface wave resonance

A Bloch surface wave (BSW) resonance configuration is introduced for biosensing with an ultra-high figure of merit (FOM). The BSW excitation is realized through the evanescent field of the core-guided fundamental mode of a side-polished photonic crystal fiber (PCF). By taking advantage of the air hole periodic microstructure of the PCF cladding, the BSW platform can be achieved with only a single high refractive index dielectric layer on its flat surface. The dielectric layer deposited on the polished surface of the PCF modifies the local effective refractive index, allowing direct manipulation of the BSWs, whereby the resonance wavelength of the surface wave can be adjusted by choosing the material and thickness of this layer. Here, we numerically investigate Bloch-like surface wave (BLSW) resonance conditions around telecom wavelengths for silicon, titanium dioxide, copper monoxide, and aluminum oxide termination layers. The BLSW excitation platform materials have low loss, which results in higher surface field enhancements and narrower resonances, which are advantageous properties for the sensors. The obtained results open new avenues for the application of optical surface waves in biosensing with high FOM. Furthermore, these results show a much higher figure of merit (FOM) than traditional approaches, allowing for increased sensitivity and accuracy.

Thermodynamic, thermoelectric and optoelectronic performances of Co2MB (M = Nb, Ta) full-heusler compounds for solar cell and UV absorber applications

An investigation for estimating the thermodynamic, thermoelectric and optoelectronic performances of Co2MB (M = Nb, Ta) full-Heusler compounds is accomplished via density functional theory within full-potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA), GGA + U (Hubbard correction), Tran-Blaha modified Becke-Johnson potentials (TB-mBJ) and spin-orbit coupling (SOC) are utilized to handle the exchange and correlation potential. The electronic band structure of Co2NbB and Co2TaB confers half-metallic nature over reasonable band gaps; 0.71 and 1.11 eV, respectively within mBJ potential. The materials are manifested with the integer values of spin magnetic moment. Further, various thermodynamic parameters under the effect of temperature and pressure have been assessed. Interestingly, Co2NbB and Co2TaB exhibit fantastic thermoelectric performances concerning high figure of merit at 1200 K. Furthermore, the computed materials are optically active and display absorption spectra in visible and more significantly in UV region of incident light. Therefore, materials can be used as good UV absorbers.

Porous pyroelectric material for waste heat harvesting

The utilization of pyroelectric materials to harvest waste heat from the ambient environment has gained much interest. However, pyroelectric energy harvesting technology still faces the challenge of low output voltage. In this paper, a porous pyroelectric ceramic with 0.3 wt.% poly(methyl methacrylate) (PMMA) as the additive was prepared via a conventional solid-state reaction technique. Our experimental results indicated that the porous PMN–PMS–PZT:0.3PMMA ceramic had a decrease in both relative permittivity and volume heat capacity at a temperature of 44ˆ∘C, compared to that of the dense sample. Additionally, the porous ceramic demonstrated an enhanced voltage responsivity from 0.50 to 0.52 m2/C and a higher figure of merit from 0.64 to 0.65 nm3/J for energy harvesting, compared to the dense sample. When 0.3 wt.% PMMA was added, the voltage generated by the device increased by 17.01% due to the presence of pores, which suggests a potential application in the field of waste heat harvesting and sensing.

Dual-channel high sensitivity photonic crystal fiber sensor based on rectangular air holes

This paper proposes a dual-channel high sensitivity photonic crystal fiber sensor with rectangular air holes, which can detect the refractive index of a single sample or detect the refractive index of two samples simultaneously, to increase the detection efficiency and wavelength sensitivity of the sample refractive index. The sensor can reduce the times of filling, emptying and cleaning of the sample to be tested and save labor and time costs. The finite element method is used to thoroughly analyze the proposed structure’s sensing properties. The results show that when the sensor detects a single sample, the maximum wavelength sensitivity is 67,300[Formula: see text]nm/RIU, and the highest figure of merit (FOM) is 547 RIU[Formula: see text]. When the sensor detects two samples synchronously, the maximum wavelength sensitivity is 64,100[Formula: see text]nm/RIU, which is the highest level among the known sensors of the same kind. It has good application prospect in the field of high sensitivity refractive index detection.

Grain refinement and polarization enhancement synergistically triggered NBT-based piezoceramics enabling sustainable high power generation

Lead-free piezoelectric energy harvesters (PEHs) with long-term stable power generation capability is an important solution for realizing reliable self-power supply of microelectronic devices such as wireless sensors. As the core of PEHs, piezoceramics with practical value require not only high figure of merit (FOM) to achieve high power generation, but also strong fracture toughness (KIC) to prevent the fracture failure caused by long-term cyclic vibration, which poses a challenge to the material design. To address these concerns, K0.5Bi0.5TiO3 was rationally introduced into Na0.5Bi0.5TiO3 matrix, and the synergistic effect of grain refinement and polarization enhancement was realized through composition design and grain size regulation to obtain excellent performance with KIC of 1.57 MPa·m1/2 and FOM of 1.94 × 10−12 m2/N. The cantilever beam-type PEH with the optimal sample achieved a high output power density of 395.5 μw/cm3, in particular, under different acceleration conditions (1g-3g), after 106 cycles, the PEH can still maintain a stable power generation output, showing a super-strong service capability. This work not only provides a class of NBT-based piezoceramics with excellent electromechanical properties, but more importantly, the design strategy associated with double synergy effect is expected to be extended to the construction of more high-quality lead-free piezoelectric devices.

Systematic first-principles investigation of electronic, optical and thermoelectric properties of all-inorganic layered ruddlesden-popper mixed halide perovskite Cs2SnI2Br2

Report on systematic study of the impact of layer dependent structural properties, electronic structures and optical characteristics on the two-dimensional (2D) Ruddlesden–Popper (RP) perovskite Cs2SnI2Br2 using first principles computation within the density functional theory method including a spin orbit coupling contribution. Our results reveal that the predicted 2D-layered RP perovskite Cs2SnI2Br2 are structurally and energetically stable which can be realized in experiments. It is also shown that the band gap and optical absorption characteristics of the 2D-layered RP perovskite Cs2SnI2Br2 are dependent on thickness variation. Interestingly, Cs2SnI2Br2 exhibited an interesting absorption coefficient in the visible region. The transport equations were solved in order to evaluate the effect of the Sn based 2D-layered RP perovskite on thermoelectric performance. It is found that Cs2SnI2Br2 has lower thermal conductivity and higher electrical conductivity for T = 300 K. In addition, Cs2SnI2Br2 is expected to get the highest figure of merit. This result provides an outstanding opportunity for this 2D RP perovskite with potential applications in solar cells and thermoelectric applications.

All-dielectric metasurface refractive index sensor with high figure of merit based on quasi-bound states in the continuum

All-Dielectric metasurfaces are widely used in the field of sense due to their small size, freedom of design, and low radiation loss. However, the optical sensor still has the problem of wide full width at half maximum (FWHM), which leads to a low figure of merit (FOM). In order to solve this problem, an all-dielectric metasurface based on quasi-bound states in the continuum (q-BIC) was proposed for refractive index sensing. The sensor structure consisted of a prism/metasurface/analyte, where the metasurface was composed of periodically arranged subwavelength asymmetric silicon gratings. The asymmetry of the structure led to the coupling of the tangential and radiative field components in the superficial layer at the resonance position, which formed a q-BIC resonance peak with a narrow FWHM in the reflection spectrum. We explained the causes of the q-BIC resonance peak generation by finite element analysis, and analyzed the factors affecting the FWHM, and also simulated the machining errors. The results showed that by reducing the asymmetry of the sensor, it could have a high FOM, with a FOM of 1.35 × 107 RIU−1. In addition, simulated machining errors within ±5 nm showed that small machining errors did not lead to the disappearance of q-BIC, which proved that the sensor had good robustness. These findings had provided ideas for the accurate detection of trace substances.

All-dielectric asymmetric planar metasurface based dual-parametric sensor

All-dielectric metasurfaces are a rapidly growing area of research because they have lower ohmic losses and sharper resonances than their metallic equivalents. In this work, we have reported a novel all-dielectric metasurface design for dual parameter (refractive index and temperature) sensing applications. The design consists of a square GaAs block on the top of a quartz substrate with a square hole etched on it. An outer cut to the GaAs block is introduced to break the symmetry. The asymmetry enables a sharp Fano resonance mode with 90% spectral contrast and extremely high quality (Q) factor of value 2.8×104 in the near-infrared (NIR) window. The multipolar nature of the high-Q resonance is studied using the cartesian multipolar decomposition technique, which reveals the electric dipolar nature of the resonance. To examine the refractive index capability of the proposed device, we varied the refractive index of the background medium and found that the device is highly sensitive and results in a very high Figure of Merit (FoM) 5384 RIU−1, owing to the very narrow linewidth of the resonance. The same design is also used for temperature sensing, which shows a notable improvement in sensitivity (72.4 pm/∘C) compared to various existing methods available. The in-depth analysis of the resonance in an optimized all-dielectric metasurface and its potential for sensing presented through this paper can be significant in designing high-performance optical sensors.

A High FoM and Low Phase Noise Edge-Injection-Based Ring Oscillator in 350 nm CMOS for Sub-GHz ADPLL Applications

This paper presents an injection locked digitally controlled ring oscillator (IL-DCRO). To reduce jitter variations, minimize oscillator spurious signals, and eliminate periodical phase error, a double edge-injection (window injection) scheme with synchronized edge directions is proposed. A combinational edge generator is utilized to substitute the sequential edge generators for injection timing requirements relaxation. By biasing devices in deep triode, digitally controlled delay cells currents are adopted for frequency tuning. This helps reducing the devices flicker (1/f) noise and minimize the DCRO overall phase noise. At 1 MHz offset of frequency, the proposed oscillator has a measured phase noise of −125.95 dBc/Hz and −115.6 dBc/Hz at oscillation frequencies of 913.4 MHz and 432.6 MHz, respectively. Fabricated in 350 nm CMOS process, with a maximum power consumption of 3.3 mW, and oscillating at 913.4 MHz, this DCRO achieves a tuned oscillator figure of merit (FoM) of −197.35 dBc/Hz. The core area of this edge-injection-based DRCO is only 0.08 mm2.

Dual-core fiber biosensor with graphene-MoS2 modification for dual-peak detection

A graphene-MoS2-based dual-core D-shaped biosensor is proposed. The sensor operates in the terahertz (THz) band and detects analytes with refractive indices from 1.33 to 1.38, encompassing most biomolecules. The accuracy of the measurement results is improved by dual-peak detection. Through optimization, the thickness of graphene is 4 times of single-layer graphene, the thickness of MoS2 is 10 µm, the thickness of the analyte is 22 µm, and the diameter of the small air hole is 52 µm. The main and secondary peaks of the sensor showed high sensitivity of 632.606 µm/RIU and 374.609 µm/RIU, respectively. Meanwhile, both the main and secondary peaks have very high figures of merit (FOM), with the highest value of 21,162.16 and 63,809.01, respectively, reflecting the sensor's excellent sensing performance. The proposed sensor provides a new idea for studying the graphene-MoS2-based dual-core biosensor.

NiTiCu shape memory alloys with ultra-low phase transformation range as solid-state phase change materials

Shape memory alloys (SMAs) have been demonstrated as effective phase change materials (PCMs) for thermal energy storage (TES) applications. NiTi and NiTiHf SMAs have shown high TES performance, as quantified by PCM figure of merit (FOM) but their use in applications requiring narrow operation temperature windows is limited by large overall phase transformation ranges (OTR). This work investigates NiTiCu SMAs as PCMs with high FOM and low OTR. A full-factorial design of experiments is used to examine 24 NiTiCu compositions. The compositions were fabricated using vacuum arc melting and their phase transformation and thermophysical properties were characterized using calorimetry, thermal diffusivity, and density measurements. The NiTiCu compositions spanned martensitic transformation temperatures between -22 and 84 °C and exhibited greater FOM (250–1050 106J2K−1s−1m−4), compared to traditional PCMs (typically <100 106J2K−1s−1m−4), with major benefits associated with higher density and higher thermal conductivity values. In addition, the NiTiCu compositions in this study show ultra-low OTR (12–20 °C) compared to NiTi and NiTiHf SMAs (>50 °C), enabling utility in narrow operating temperature windows. Thermal cycling was also performed revealing extreme stability of martensitic transformation with only 0.04 °C shift in transformation temperatures after 80 thermal cycles, which is the lowest reported to date in SMA literature.

Inhibiting Mg Diffusion and Evaporation by Forming Mg-Rich Reservoir at Grain Boundaries Improves the Thermal Stability of N-Type Mg3 Sb2 Thermoelectrics.

N-type Mg3 Sb2 -based thermoelectric materials show great promise in power generation due to their mechanical robustness, low cost of Mg, and high figure of merit (ZT) over a wide range of temperatures. However, their poor thermal stability hinders their practical applications. Here, MgB2 is introduced to improve the thermal stability of n-type Mg3 Sb2 . Enabled by MgB2 decomposition, extra Mg can be released into the matrix for Mg compensation thermodynamically, and secondary phases of Mg─B compounds can kinetically prevent Mg diffusion along grain boundaries. These synergetic effects inhibit the formation of Mg vacancies at elevated temperatures, thereby enhancing the thermal stability of n-type Mg3 Sb2 . Consequently, the Mg3.05 (Sb0.75 Bi0.25 )1.99 Te0.01 (MgB2 )0.03 sample exhibits negligible variation in thermoelectric performance during the 120-hour continuous measurement at 673 K. Moreover, the ZT of n-type Mg3 Sb2 can be maintained by adding MgB2 , reaching a high average ZT of ≈1.1 within 300-723K. An eight-pair Mg3 Sb2 -GeTe-based thermoelectric device is also fabricated, achieving an energy conversion efficiency of ≈5.7% at a temperature difference of 438 K with good thermal stability. This work paves a new way to enhance the long-term thermal stability of n-type Mg3 Sb2 -based alloys and other thermoelectrics for practical applications.

A Mid-Infrared Multifunctional Optical Device Based on Fiber Integrated Metasurfaces.

A metasurface is a two-dimensional structure with a subwavelength thickness that can be used to control electromagnetic waves. The integration of optical fibers and metasurfaces has received much attention in recent years. This integrated device has high flexibility and versatility. We propose an optical device based on fiber-integrated metasurfaces in the mid-infrared, which uses a hollow core anti-resonant fiber (HC-ARF) to confine light transmission in an air core. The integrated bilayer metasurfaces at the fiber end face can achieve transmissive modulation of the optical field emitted from the HC-ARF, and the Fano resonance excited by the metasurface can also be used to achieve refractive index (RI) sensing with high sensitivity and high figure of merit (FOM) in the mid-infrared band. In addition, we introduce a polydimethylsiloxane (PDMS) layer between the two metasurfaces; thus, we can achieve tunable function through temperature. This provides an integrated fiber multifunctional optical device in the mid-infrared band, which is expected to play an important role in the fields of high-power mid-infrared lasers, mid-infrared laser biomedicine, and gas trace detection.

Amplification and Dynamic Control of Circularly Polarized Luminescence in Poly (vinyl Alcohol)/CdSe@CdS Nanorod Assembly Twisted‐Stacking Hetero‐Structures

AbstractChiroptical materials with strong and switchable circularly polarized luminescence (CPL) properties have gained considerable interest due to their feasible applications in optoelectronic devices, sensing, and information encryption. However, in most cases, their luminescence dissymmetry factor (glum) and figure of merit (FOM) values remain very low. Herein, a novel heterogeneous twisted‐stacking structure is proposed, which endows with strong CPL amplification (a maximum of ≈15‐fold enhancement) over traditional homogeneous structures and a high FOM value up to 0.11. Interestingly, their CPL performance (including the sign, magnitude, and spectral position) and the FOM values can be precisely manipulated or even inversed by simply uniaxial stretching, since the phase retardation of the anisotropic poly (vinyl alcohol) layer can be controlled. Moreover, by combining with the viologen gel electrochromic system, the in situ voltage‐driven switching and patterning of the CPL signal can be successfully achieved, with low operation voltage and good cycling stability. This study provides a creative strategy for fabricating strong and electrical switchable CPL‐active materials, which promise new opportunities in miniaturized smart electrochiroptical devices for future information technology.

Excitation of surface plasmon resonance with sodium-based photonic crystal fiber for sensing applications

Surface plasmon resonance (SPR) sensors using precious metal excitation have encountered bottlenecks in performance enhancement. To address this issue, we propose a photonic crystal fiber (PCF) sensor that utilizes a polymer-protected sodium film to excite the SPR effect. The PCF has hexagonally arranged air holes and a polishing plane. The sodium film is deposited on the polished plane and protected with polymethyl methacrylate or polydimethylsiloxane for refractive index sensing or temperature sensing. We analyzed this structure using the finite element method and found that the sodium-based SPR sensor has greater sensitivity, wider detection range, and higher figure of merit (FOM) than the SPR sensor using precious metal excitation. Numerical results showed that the maximum sensitivity was 35,400 nm/RIU, the widest detection range was 1.22–1.42, and the highest FOM was 3550RIU−1 at different sodium film thicknesses. When applied to temperature sensing, its maximum sensitivity is 20.5 nm/°C, and the temperature detection range is 0°C–100°C. In addition, our proposed sodium-based SPR fiber sensor is compatible with a thermo-assisted spin-coating process, so a good guideline scheme is available for the preparation. Therefore, our proposed sensor shows excellent potential in sensing and expands the application range of sodium-based plasma devices.

A high-performance long-range surface plasmon resonance sensor based on the co-modification of carbon nanotubes and gold nanorods

In order to solve the problem that the sensitivity of the optical fiber surface plasmon resonance (SPR) sensor is limited and the full width at half maxima (FWHM) is greatly increased after modification of two-dimensional materials such as carbon nanotubes (CNTs), this paper proposes a Long-Range Surface Plasmon Resonance (LRSPR) Sensors co-modified by CNTs and gold nanorods. Gold nanorods were used to further enhance the sensitivity, and a simple and convenient method was used to excite the LRSPR by using low refractive index UV glue as a dielectric matching layer (DML). Compared with SPR sensor, the FWHM is reduced. The LRSPR sensor produced in this paper has a sensitivity of 5056.35 nm/RIU and a figure of merit (FOM) of 23.52 RIU−1, which are 150.64% and 24.38% higher than conventional SPR sensors, providing a method to achieve high sensitivity and FOM of the sensor. At the same time, the large specific surface area of CNTs and gold nanorods can also improve the biocompatibility of the sensor surface, which makes it have the potential of biosensing. In this paper, the use of UV glue as a DML to excite LRSPR is proposed for the first time.

3D Printing of Bi2Te3-Based Thermoelectric Materials with High Performance and Shape Controllability.

Thermoelectric (TE) energy conversion technology provides a promising way to improve the efficiency of fossil energy by generating electricity from low-grade waste heat. With regard to these applications, thermoelectric generators (TEGs) should be designed from system integration perspectives to simultaneously improve heat transfer efficiency and system simplification as well as the robust mechanical properties. However, typical TEGs fabricated by conventional methods barely accomplish such requirements. Herein, high-quality TEGs were assembled by combining the well-flowable spherical bismuth telluride (BT) powdered precursors and selective laser melting (SLM) technology. By optimizing the electronic and phonon transport properties through defect engineering driven by 3D printing, a high figure of merit was accomplished for 1.27 (p-type) and 1.13 (n-type) in BT. This achievement is primarily attributed to the nonequilibrium solidification mechanism, which leads to the formation of multiscale defects during the 3D printing process. The introduction of these multiscale defects enables the effective scattering of wide frequency phonons, leading to a substantial reduction in lattice thermal conductivity. Meanwhile, robust mechanical properties were obtained in the printed p-type/n-type BT TE materials parallel to the building direction (BD) with a compressive strength reaching 257/250 MPa by employing the fine grain structure and the high density of nanotwins introduced during the SLM process. A well shape-controllable and high-performance TEG was designed using 3D-printed BT half-rings, and an output power of 134 mW was achieved at a temperature gradient of 38.9 °C. Our study opens a new route for the great potential of TE materials based on standard commercial SLM 3D printing technology for low-grade waste heat emitted from structures with heterogeneous shapes.