High Figure Of Merit Research Articles

Layered PrZnOX (X = P, As) compounds: Promising n-type thermoelectric materials with low lattice thermal conductivity

The heteronanionic materials exhibit low lattice thermal conductivities and excellent electronic transport properties on account of their unique ZrSiCuAs-type crystal structures. In this study, the thermoelectric (TE) properties of the layered PrZnOX (X = P, As) compounds are theoretically elaborated in combination with the first-principles calculations and Boltzmann transport theory. The layered PrZnOP and PrZnOAs compounds are direct semiconductors with wide bandgaps of 1.96 eV and 1.88 eV within HSE06 hybrid functional, respectively. Through a comprehensive evaluation of the crystal structures and mechanical properties, the PrZnOX (X = P, As) compounds are thermodynamically and mechanically stable. The lattice thermal conductivities are 3.60 W/mK and 3.26 W/mK for the PrZnOP and PrZnOAs compounds at 300 K, respectively. The n-type layered PrZnOX (X = P, As) compounds exhibit large power factors on account of the high electrical conductivities and large Seebeck coefficients compared to the p-type situations. Consequently, the high figure of merits (ZTs) of 1.88 and 1.78 at 1000 K are discovered for the n-type PrZnOX (X = P, As) compounds. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties of PrZnOX (X = P, As) materials, but also elaborates the potential TE application of heteroanionic material at high temperature.

Enhanced thermoelectric performance of a wide-bandgap twisted heterostructure of graphene and boron nitride.

The manipulation of the relative twist angle between consecutive layers in two-dimensional (2D) materials dramatically modulates their electronic characteristics. Twisted bilayer graphene (tblg) and twisted boron nitride (tBN) exhibit Moiré patterns that have the potential to revolutionize various fields, from electronics to quantum materials. Here, the electronic and thermoelectric properties of 21.8° tblg and 21.8° tBN and a 21.8° twisted graphene/boron nitride (Gr/BN) heterostructure were investigated using density functional theory and Boltzmann transport theory. The twisted Gr/BN heterostructure possesses a wide band gap of 1.95 eV, which overcomes the limitations of the absence of a band gap of graphene and boron nitride's extremely wide band gap. A significant increase in thermoelectric power factor was obtained for the heterostructure compared to its parent materials, 21.8° tblg and 21.8° tBN. It has a thermal conductivity of 5.88 W m-1 K-1 at 300 K, which is much lower than those of 21.8° tblg and 21.8° tBN. It is observed that graphene plays an important role in electron transport or power factor enhancement, whereas BN helps in reducing the thermal conductivity in twisted Gr/BN systems. A strong role of boundary scattering in thermal transport compared to electrical transport was observed. A high figure of merit (ZT) of 1.28 for the twisted Gr/BN heterostructure at a ribbon width of L = 10 nm and T = 900 K was obtained. This suggests its suitability as an effective material for thermoelectric applications.

Determination of thermal conductivity in nano-oxides under the effect of size, dimension and thermal Kapitza resistance

The author has proposed a simple model to determine the effective thermal conductivity variance in nanomaterials with respect to size under Kapitza thermal resistance effect. The formulation is based on the relation of thermal conductivity with specific heat, sound velocity and mean free path in nanosolids. Using the Jiang’s qualitative approach for melting temperature variation in nanomaterials with dimension and size;the thermal conductivity expression for nanosolids is formulated. Effective thermal conductivity of nanosolid is determined on the basis of effective medium approach. The results obtained from formulation depicts the increase in Effective thermal conductivity of nanomaterial with increase in its size. The present model results are seen in good consistency with the available data of previous workers and matches the variation trend as predicted previously. The exponential drop in thermal conductivity of nanomaterials with their size reduction to nanoscale make them efficient material to be use in thermoelectric devices because of their high figure of merit.

All-dielectric metasurface two-parameter sensor based on quasi-bound states in continuum

<sec>Refractive index sensors based on metal metasurfaces are commonly limited by their low quality factors due to significant Ohmic losses in the metal material. In contrast, sensors based on all-dielectric metasurfaces can overcome this disadvantage. Currently, all-dielectric metesurface sensors based on symmetry-protected bound states in the continuum (BIC) have aroused intense research interest due to their ability to achieve ultrahigh quality factors. Such a metasurface sensor is mainly based on single BIC and single form of symmetry breaking. There are few studies on metasurface sensors of multiple BICs and multiple forms of symmetry breaking. In additon, the refractive-index sensors commonly neglect the influence of temperature fluctuation and thus suffer the crosstalk between the refractive index and temperature of the environment.</sec><sec>In this work, an all-dielectric metasurface composed of a periodic array of asymmetric semicircular-cylinder pairs is designed and two quasi-bound states in the continuum (QBIC) with high quality factors are obtained. By choosing three different forms of symmetry breaking (two in-plane and one out-of-plane), two robust QBIC modes can be generated in the selected near-infrared frequency band, and their resonance wavelengths, quality factors and polarization dependences exhibit different characteristics. Full-wave simulation results show that by measuring the resonance wavelengths of the two QBICs (denoted by QBIC1 and QBIC2), two-parameter sensing of refractive index and temperature can be achieved, which then solves the problem of crosstalk between the refractive index and temperature of the environment in refractive-index sensing. The dependence of quality factor on asymmetric parameters follows an inverse quadratic relation for the two QBICs. By adjusting the asymmetric parameters, the quality factor can be theoretially increased to any value, so that the sensing performance can be improved and adjusted. For refractive-index sensing, the QBIC1 can achieve a sensitivity of 194.7 nm/RIU and a highest figure of merit (FOM) of 8197 (corresponding to a quality factor of 45829); the QBIC2 can achieve a sensitivity of 170 nm/RIU, and a highest FOM of 4970 (corresponding to a quality factor of 28097). For temperature sensing, the QBIC1 can achieve a sensitivity of 7.77 pm/℃, and the QBIC2 can achieve a sensitivity of 24 pm/℃.</sec>

GeSe-embedded metal-oxide double heterojunctions for facilitating self-biased and efficient NIR photodetection.

Infrared radiation detection is significantly important in communication, imaging, and sensing fields. Here, we present the integration of germanium selenide (GeSe) with a metal-oxide heterojunction to achieve efficient near-infrared (850 nm) photodetection under zero bias conditions. Nickel oxide (NiO) and silicon (Si) formed a favorable energy band alignment for the efficient separation of photogenerated charge carriers, resulting in a high figure of merits. The additional incorporation of a germanium selenide (GeSe) interlayer between the nickel oxide (NiO) and silicon (Si) heterojunction improved the external responsivity (from 0.22 to 3300 mA W-1), detectivity (from 1.24 × 107 to 20 × 109 Jones), normalized photocurrent to dark current ratio (from 4 × 103 to 3 × 105 W-1), noise equivalent power (from nW to pW), and rise/fall time (from 34/34.5 ms to 14/13 ms). The interlayer introduction of a semiconductor in various heterojunctions can facilitate self-biased and broadband photodetection for widely used optoelectronic applications.

Rare earth-based oxides double perovskites A2NiMnO6 (A= La and gd): Applications in magneto-caloric, photo-catalytic and thermoelectric devices

In this paper, we have conducted theoretical work on rare earth-based double perovskites namely, La2NiMnO6 and Gd2NiMnO6, using generalized gradient approximation (GGA) and GGA + U formulations within the full potential linearized augmented plane wave (FP-LAPW) method. It is revealed that using GGA + U computations instead of the conventional GGA method results in a reasonable widening of the band gaps and best fit with the previously explored experimental data with U = 1.5 eV. Further, the band gap values are increased with increasing the U values for the 3d states of Ni and Mn. Moreover, we found that these materials show high magnetic moment, high absorption in the visible and ultraviolet region, and high figure of merit (nearly one for Gd2NiMnO6 at room temperature), hence show their potential in multiple applications such as magneto-caloric, photo-catalytic, solar energy, and thermoelectric devices.

Impact of Various Dopants on Thermoelectric Transport Properties of Polycrystalline GeSb2Te4

GeSb2Te4 (GST124), one of the well‐known phase‐change materials for nonvolatile memory and rewritable optical storage, has been recently found to be promising thermoelectric materials with low lattice thermal conductivity and high electrical conductivity. However, its thermoelectric performance is greatly restricted by the excessively high hole concentration. Herein, the impact of a series of group IIIA (Al, Ga, In) and group VIA (S, Se) dopants on the electrical transport properties of polycrystalline GST124 has been studied. It is found that element sulfur (S) has the best doping efficiency because the GeS bonds are very strong and ionic that are beneficial for suppressing Ge vacancies to reduce the carrier concentration. Meanwhile, element indium (In) also shows decent doping efficiency because its ionic radius is close to the Ge ion and the InTe bonds have moderate bonding strength. Moreover, In doping introduces a resonant level in the valence band, leading to enhanced Seebeck coefficient and power factor. A high figure of merit (zT)of 0.73 at 700 K and an average zT of 0.48 over 300–750 K are obtained in Ge0.92In0.08Sb2Te4, which are 26% and 66% higher than pristine GST124. This study will advance the understanding and development of high‐performance GeSbTe‐based thermoelectric materials.

Fine-tuning SnO2 films: Unleashing their potential through deposition temperature optimization by ultrasonic spray pyrolysis

In this study, the optimization of the deposition temperature, which directly affects the crystallinity, morphology, and electrical conductivity of SnO2 films deposited onto Corning Eagle XG glass substrates using the ultrasonic spray pyrolysis technique, was investigated to tailor their physical properties for various applications. Structural analyses revealed that the films had a tetragonal rutile structure, and while films deposited at lower temperatures exhibited a higher prevalence of (200) oriented planes, yet this decreased with an increase in deposition temperature. Morphological analyses showed that the films consisted of grains with octahedral shapes, and films deposited at lower temperatures were found to be more compact. The films had bandgap energy ranges between 3.96 eV and 4.02 eV. Hall effect measurements revealed that not only the carrier concentration decreased from 4.52 × 1019 cm−3 to 0.80 × 1019 cm−3, but the mobility also decreased from 23.32 cm2/Vs to 12.85 cm2/Vs. Among all the films, it was noted that the films deposited at 350 °C had the highest figure of merit which is 12.3 × 10−4 Ω−1. It can be concluded that the changes underlying these variations are associated with structural and morphological changes depending on the substrate temperature. Also, significant results have been attained in applications where precise control over crystal structure and surface morphology is crucial.

Toroidal Dipole All-Dielectric Metasurfaces with High Sensitivity, High Figure of Merit, and Robustness for Refractive Index Sensing

Toroidal Dipole All-Dielectric Metasurfaces with High Sensitivity, High Figure of Merit, and Robustness for Refractive Index Sensing

Ultra-high-Q and ultra-sensitive refractive index sensing in low refractive index dielectric gratings based on bound states in the continuum

The realization of a high quality factor (Q-factor) and strong local optical fields has long been of great interest in the field of nanophotonics. Unfortunately, it is still challenging to achieve high-Q and strong localized fields in nanostructures made of low refractive index materials. In this study, drawing upon the concept of bound states in the continuum (BICs), an asymmetric dielectric grating composed of low refractive index materials is demonstrated to generate an ultra-high-Q symmetry-protected quasi-BIC in the visible wavelength. Importantly, the design of BIC (quasi-BIC) mode enables the strong localized confinement of light in air. By leveraging this property, we realize ultra-sensitive refractive index sensing with a remarkable sensitivity of 669 nm/RIU and a high figure of merit (FOM) of 45,314RIU−1. This study offers an approach to achieve highly sensitive and high precision refractive index sensing with potential applications in the practical realization of strong light–matter interactions using low index materials.

High-Sensitivity Temperature Sensor Based on Photonic Crystal Fiber Filled with Ethanol and Toluene

A surface plasmon resonance photonic crystal fiber-based highly sensitive temperature sensor is proposed. The surface plasmon resonance is induced by injecting toluene into the central hole and ethanol into the side holes coated with gold film. Optimal sensor sensitivity by optimizing the size and position of the air holes. The coupling mechanism and sensing performance of the proposed sensor are analyzed. The results indicate that in the sensing range of 0 °C−70 °C, the highest figure of merit (FOM) is 0.1169/°C and the average temperature sensitivity can reach 7.13 nm/°C. Such temperature sensor exhibits tremendous potential in the domain of temperature detection.

Achieving High Core Neuron Density in a Neuromorphic Chip Through Trade-off Among Area, Power Consumption, and Data Access Bandwidth.

As a crucial component of neuromorphic chips, on-chip memory usually occupies most of the on-chip resources and limits the improvement of neuron density. The alternative of using off-chip memory may result in additional power consumption or even a bottleneck for off-chip data access. This article proposes an on- and off-chip co-design approach and a figure of merit (FOM) to achieve a trade-off between chip area, power consumption, and data access bandwidth. By evaluating the FOM of each design scheme, the scheme with the highest FOM (1.085× better than the baseline) is adopted to design a neuromorphic chip. Deep multiplexing and weight-sharing technologies are used to reduce on-chip resource overhead and data access pressure. A hybrid memory design method is proposed to optimize on- and off-chip memory distribution, which reduces on-chip storage pressure and total power consumption by 92.88% and 27.86%, respectively, while avoiding the explosion of off-chip access bandwidth. The co-designed neuromorphic chip with ten cores fabricated under standard 55 nm CMOS technology has an area of 4.4 mm 2 and a core neuron density of 4.92 K/mm 2, an improvement of 3.39 ∼30.56× compared with previous works. After deploying a full-connected and a convolution-based spiking neural network (SNN) for ECG signal recognition, the neuromorphic chip achieves 92% and 95% accuracy, respectively. This work provides a new path for developing high-density and large-scale neuromorphic chips.

Mismatch error compensation of hybrid CS‐DAC to achieve high figure of merit utilizing on‐chip self‐healing assisted swap‐enabled randomization technique

SummaryThe process and design variations during fabrication generate random mismatch‐induced nonlinearities in Current steering DACs (CS‐DACs), which are the main reason for performance degradation. Considering this, a mismatch error compensation method is highly desirable to boost both static and dynamic performances for the wide‐band CS‐DACs. To address this issue, an on‐chip self‐healing assisted swap‐enabled randomization technique (SASR) is proposed in this work for the Nyquist band CS‐DAC structures. This paper presents a robust hybrid CS‐DAC architecture to enhance both static and dynamic performances. The partial self‐healing method measures and recovers the mismatch current of the current cells. Further, to reduce the mismatch‐based nonlinear distortions, swap‐enabled randomization technique is adopted. This enhances the high‐frequency spurious‐free dynamic range (SFDR) values by mitigating inter and intra‐segment mismatch errors. A higher figure of merit (FoM) is obtained for 10‐bit CS‐DAC architecture utilizing the proposed SASR technique compared with state‐of‐the‐art DACs, which indicates the suitability for higher precision and high‐speed CS‐DAC structures.

Graphene-integrated hybrid plasmonic waveguide for Kerr nonlinear application

Graphene, with its broadband optical properties and high optical nonlinearity, shows promise as an ultrathin material compatible with CMOS technology for all-optical signal processing in integrated photonics. This paper presents simulation, analysis, and design of a novel graphene-integrated nonlinear hybrid plasmonic waveguide. Finite element simulations study the Kerr nonlinear effect of extra graphene layers. The enhanced nonlinear parameter of [Formula: see text][Formula: see text]W[Formula: see text][Formula: see text]Km[Formula: see text] and nonlinear figure-of-merit (FOM) of 2.10 achieved at 1,550[Formula: see text]nm exceed those of silicon-on-insulator (SOI) hybrid plasmonic waveguides. The proposed graphene-integrated hybrid plasmonic waveguide (GHPW) demonstrates high Kerr nonlinearity and FOM, indicating potential for nonlinear all-optical signal processing.

First principle examination of two dimensional rare-earth metal germanide halides Y2GeX2 (X = Cl, Br, I) for thermoelectric applications

In the present work electronic, structural and thermoelectric properties of newly designed layered rare-earth metal germanide halides such as Y2GeX2 (X = Cl, Br, I) are investigated. These materials are indirect band gap semiconductors with narrow band gap 0.30 eV for Y2GeCl2,0.36 eV for Y2 GeBr2, and 0.41 eV for Y2GeI2 respectively. First principles method along with Boltzmann transport equations (BTE) is utilized together to analyse the thermoelectric properties. These materials are dynamically and mechanically stable. Thermoelectric coefficients such as electrical conductivity, seebeck coefficient and thermal conductivity are computed and put together to ultimately get the Figure of merit (ZT). Y2GeI2 has highest figure of merit (ZT) of 0.42 with Seebeck coefficient 532.12 VK−1, electrical conductivity 8.6 ×105Sm−1 and has lowest lattice thermal conductivity value of 5.55 Wm−1K−1 among three materials, which is necessary to achieve high figure of merit. The computed value of Figure of merit 0.07, 0.22 and 0.42 for Y2GeCl2, Y2GeBr2 and Y2GeI2 accordingly, shows that these materials can be considered as good candidates for energy harvesting in thermoelectric applications.

A comparative analysis of fiber-based surface plasmonic resonance sensors utilizing various fluoride glass cores and the influence of different oxide layers on the sensor performance in near-infrared

In a fiber-based surface plasmon resonance (SPR) sensor, with multiple layers, including fluoride glass core, cladding, metal (Ag), graphene and alcohols as the analyte, we focused on comparing the effects of 12 different types of fluoride glass cores from three main groups of fluorozirconate (ZrF4-based), fluoroaluminate (AlF3-based) and fluoroindate (InF3-based). The comparison was conducted to evaluate the sensor’s sensitivity and figure of merit (FOM) at specific near infrared (NIR) wavelengths (785 nm, 852 nm, 895 nm and 980 nm) while keeping other parameters constant. The highest FOM was consistently observed at the wavelength of 980 nm for all three categories of fluoride glass cores. Among them, the fluoride glass core IZBSC (40 InF3-20 ZnF2-15 BaF2-20 SrF2-5 CaF2) from InF3-based group presented the largest FOM = 1459.15 RIU−1. Furthermore, we observed that the FOM of the fiber types belonging to the ZrF4-based and InF3-based categories increased with the wavelength. However, the fluoroaluminate fibers showed different trend and they also exhibited the smallest FOM values at 852 nm, 895 nm and 980 nm wavelengths. To enhance the sensor’s performance, we explored the incorporation of an oxide layer into the to the SPR sensor with a ZBLAN (55.8 ZrF4-14.4 BaF2-5.8 LaF3-3.8 AlF3-20.2 NaF) core. We analyzed the effects of various oxide coatings (Sc2O3, Lu2O3, Al2O3, GeO2, TeO2, Ta2O5, MgO, TiO2, and ZnO) on the Ag layer, which has not previously studied, to the best of our knowledge. Among the different oxide coatings, the Ta2O5 layer, with optimized thickness, exhibited a significant enhancement, achieving FOM of 1631.43 RIU−1.

Modeling and simulation of multifaceted properties of X2NaIO6 (X = Ca and Sr) double perovskite oxides for advanced technological applications.

In this study, the authors have investigated the structural, optoelectronic, thermoelectric, and thermodynamic properties of Ca2NaIO6 and Sr2NaIO6 double perovskite oxides. Both materials exhibit semiconductor behavior with direct band gaps (Eg) of 0.353eV and 0.263eV, respectively. Optical parameters like absorption coefficient α(ω), reflectivity R(ω), dielectric constants, and refractive index have been calculated. The most notable absorption peaks are identified at 5.52eV (equal to 108.33 × 104cm-1) in the case of Ca2NaIO6 and at 11.16eV (equivalent to 118.17 × 104cm-1) for Sr2NaIO6. These findings suggest a promising outlook for applications in optoelectronics. Moreover, their commendably low thermal conductivity and a high figure of merit, particularly at low temperatures (100K), indicate their effectiveness as thermoelectric materials. This analysis underscores that these materials hold potential as suitable candidates for n-type doping, making them well-suited for use in thermoelectric devices. Studying thermal properties, including thermal expansion, bulk modulus, acoustic Debye temperature, entropy, and heat capacity, contributes to understanding the materials' thermodynamic stability. The titled materials are dynamically stable. The analysis of these double perovskite materials highlights their potential across various technological applications due to their advantageous structural, electronic, optical, and transport properties, offering new possibilities in material science and technology development. The study utilized the full potential linearized augmented plane wave (FP-LAPW) method in conjunction with density functional theory within the WIEN2k simulation code. This approach is widely recognized as one of the most dependable methods for evaluating the photovoltaic characteristics of semiconducting perovskites. The thermoelectric properties were ascertained using the rigid band approach and the constant scattering time approximation, both implemented in the BoltzTraP computational code.

Engineering the Intrinsic Chirality of Plasmonic Au@Pd Metamaterials for Highly Sensitive Chiroplasmonic Hydrogen Sensing.

Metal helicoid nanoparticles with intrinsic 3D chiral structures have emerged as a new class of plasmonic metamaterials with outstanding chiroplasmonic properties. Despite the considerable potential of metal helicoid nanoparticles in chiroplasmonic sensing, their sensing capabilities remain elusive, stressing the need for the rational chirality engineering of helicoid nanoparticles. In this report, Au@Pd helicoid nanoparticles with engineered chiroplasmonic properties and integrated hydrogen sensing capabilities are rationally synthesized. As chiroplasmonic metamaterials, the Au@Pd helicoid nanoparticles exhibit unprecedented sensitivity for hydrogen chiroplasmonic sensing in the visible range. A significant circular dichroism red-shift as large as 206.1nm can be achieved when they are exposed to hydrogen. Such a high sensitivity outperforms all the plasmonic hydrogen sensors in the visible range. Besides sensitivity, the chiroplasmonic sensing platform shows a good linear range of 1.5-6.0% hydrogen concentration with higher figure of merit, excellent selectivity, and good reusability. To further demonstrate its applicability, this chiroplasmonic hydrogen sensing platform is utilized to investigate hydrogen absorption and desorption kinetics on Pd. This study heralds a new paradigm for plasmonic hydrogen sensing and highlights the tremendous potential of utilizing helicoid nanoparticles as chiroplasmonic sensing metamaterials by chirality engineering.

Finite-element modeling of a perovskite-based symmetric plasmonic waveguide with deep-subwavelength confinement and high figure of merit

The two-dimensional perovskites are emerging as an excellent material platform for various optoelectronic devices such as solar cells, lasers, and photodetectors. Here, by combining perovskite materials and plasmonic materials, a hybrid plasmonic waveguide with perovskite layers serving as the low index materials is proposed. The modal characteristics, fabrication error tolerance, and integration performance of this structure are studied by using the finite element method at the wavelength of 1550 nm. The results show that the proposed waveguide exhibits the strong field confinement ability and high figure of merit. Moreover, the proposed waveguide shows a relatively high tolerance to fabrication errors, and exhibits an extremely low crosstalk, which is quite suitable for applications in the compact photonic integration.

Ultralow in-plane thermal conductivity of [formula omitted] nanobelts prepared by magnetron sputtering

As a thermoelectric material, Cu2-xSe has attracted much attention due to its low thermal conductivity and high figure of merit. The improvement of thermoelectric performance of Cu2-xSe is dominated by reducing thermal conductivity, such as doping and preparation of nanopores. However, there is little research on the thermal conductivity of Cu2-xSe nanostructures. This paper uses magnetron sputtering to prepare Cu2-xSe films on photoresist substrates, and characterizes the material properties by TEM, GIXRD, and XPS. Simultaneously, we successfully prepared Cu2-xSe nanobelts attached on MEMS suspended devices, combined with FIB and tungsten probe for cutting and transfer. The steady-state method was used for the first time to measure the thermal conductivity of Cu2-xSe nanobelts from low temperature to phase transition. Due to the strong interface and boundary scattering of the nanobelts, Cu2-xSe exhibits a thermal conductivity as low as 0.32 W/(m·K), which provides a possibility for improving thermoelectric performance near phase transition. Furthermore, at the phase transition, the temperature difference between the two suspended islands leads to mixed phase of Cu2-xSe nanobelts, which shows broad prospects for thermal regulation.