Energy Bandwidth Research Articles

Exotic quantum states in multilayer phosphorene nanoribbons in electric and magnetic fields

Using the tight-binding method, we modeled the energy spectra of multilayer phosphorene nanoribbons in a perpendicular electric field and in-plane magnetic field. Phosphorene nanosheets have a highly anisotropic honeycomb-like lattice. Their band gap is wider than that of their bulk counterparts, and armchair and zigzag edges of either skewed or regular type terminate the nanowire edges. Zigzag and various skewed edges support states whose wave functions decay exponentially from an edge. These states are virtually dispersionless and split the band gap. In principle, regular armchair edges do not host edge states. Thus, the energy spectrum in this case has a wide band gap. Here, we consider nanoribbons composed of multilayer phosphorene with regular armchair edges. A wide direct energy band gap exists when external fields are absent, but its width decreases when a perpendicular electric field is applied. The Dirac-like cones cross-section emerges at the zone center for a particular field value, named the lowest critical field. Although spin–orbit coupling was not included in the model, there is a small gap at the anticrossing site. The local density of states shows that the conduction- and valence-band states near the anticrossing are localized on the top and bottom surfaces of the nanoribbon. A thorough analysis of the interlayer coupling integrals indicates that for sufficiently thin phosphorene slabs, the electron and hole states at the opposite sides of the slab couple mutually strongly, despite the tendency of an external electric field to separate them. A further increase in the electric field induces an inversion between the conduction and valence band states in the zone center, which is inherent to topological insulators. However, sharp anticrossings at the zone center emerged for certain higher field values, named higher critical fields. Furthermore, when an in-plane magnetic field is applied, the conduction and valence band states shift, causing the dispersion to twist around the center of the k-space. Therefore, the band gap is indirect and closes for a sufficiently large magnetic field. A similar effect is observed in quantum spin Hall insulators, in which an in-plane magnetic field induces a semiconductor-to-semimetal transition. We conclude that the band inversion and topological-like features induced by external fields can be attributed to the strong interlayer coupling inherent to multilayered materials with anisotropic honeycomb lattices.

A Heterogeneous Microprocessor Based on All-Digital Compute-in-Memory for End-to-End AIoT Inference

Deploying neural network (NN) models on Internet-of-Things (IoT) devices is important to enable artificial intelligence (AI) on the edge realizing AI-of-Things (AIoT). However, high energy consumption and bandwidth requirement of NN models restricts AI applications on battery-limited equipments. Compute-In-Memory (CIM), featured with high energy efficiency, provides new opportunities for the IoT deployment of NN. However, the design of CIM-based full system is still at the early stage, lacking system-level demonstration and vertical optimization for running end-to-end AI applications. In this paper, we demonstrate a low-power heterogeneous microprocessor System-on-Chip (SoC) with an all-digital SRAM CIM accelerator and rich data acquisition interfaces for end-to-end AIoT NN inference. A dedicated reconfigurable dataflow controller for CIM computation greatly lowers bandwidth requirement on the system bus and improves execution efficiency. The all-digital SRAM CIM array embeds NAND-based bit-serial multiplication within the readout sense amplifier balancing the storage density and system-level throughput. Our chip achieves a throughput of 12.8 GOPS, with 10 TOPS/W energy efficiency. Benchmarked by the four tasks in MLPerf Tiny, experimental results show 1.8x to 2.9x inference speedup over a baseline CIM processor.

Extended-bandwidth solar nano-concentrator integrated with graphene-metamaterial for photovoltaic energy harvesting applications

Concentration photovoltaics are used to achieve solar energy focusing on small-area solar cells, thus obtaining a high efficiency at a reasonable cost. An array of gold plasmonic concentrator cells is proposed here, which can nano-focus the solar radiation down to 60 nm spot size. It works over the entire solar energy bandwidth up to 2400 nm wavelength, which is extended beyond the conventional solar cells known maximum operating wavelength of 1800 nm. The concentrator consists of a coaxial waveguide with a tapered section that can plasmonically nano-focus solar radiation, followed by a straight waveguide section to propagate focused light along a graphene metamaterial for optical absorption. The metamaterial is integrated within the 60 nm gap of the straight waveguide section. The metamaterial consists of 10 concentric graphene shell layers, which are cross-connected by 5 horizontal graphene annuli. The concentrator and metamaterial design maximizes the solar optical absorption efficiency within the graphene metamaterial. The graphene optical absorption is enhanced up to 27 times with an almost flat response covering most of the solar bandwidth. The plasmonic absorption within the gold surfaces of the structure is found to be reasonable. The enhanced optical absorption of the weak solar radiation received within the extended band (1800–2400 nm) can reach up to 50%. The concentrator device is polarization insensitive with a 120o field-of-view. The enhanced optical power absorption in graphene metamaterial could be used in photovoltaic energy harvesting applications.

Broadband energy harvesting in a two-degree-of-freedom nonlinear system without internal resonance

In this paper, we propose a novel two-degree-of-freedom (TDOF) nonlinear energy harvester without internal resonance to realize broadband harvesting characteristic. To show the performance, a TDOF nonlinear electromagnetic harvester is designed. The electromechanical coupling system is established and solved by adopting the harmonic balance method. The modulation equations are constructed, the first-order harmonic solutions of the system are obtained and the frequency response curves of the displacement and current are plotted. The advantage of the proposed harvester is compared to the conventional single-degree-of-freedom (SDOF) nonlinear model and the corresponding TDOF linear system, the results achieve that the proposed scheme can enhance the bandwidth of the harvesting energy. Furthermore, the influences of system parameters on the response are discussed. The accuracy of the first-order harmonic results is revealed by numerical simulations. To further demonstrate the accuracy of analytical solutions, the finite element simulation is constructed in ANSYS finite element analysis (FEA) software. The performance predictions from the analytical solutions are compared with results from FEA. It is convincingly demonstrated that periodic solutions have a degree of good consistency for the behavior of frequency response curves.

Enhancement of optical properties of two-dimensional Bi2Te2Se by biaxial strain based on first-principles

The study of two-dimensional flexible materials in mechanic and optics has gained significant attention. By applying strain to modify the internal structure of materials, researchers can investigate the resulting mechanical and optical changes, offering exciting opportunities for further exploration in this field. The electronic structure, mechanical properties, and optical properties of the two-dimensional trigonal system Bi2Te2Se under biaxial strain regulation were investigated by using the first-principles plane pseudopotential plane wave method based on density generalized function theory. The analysis reveals that the energy bandwidth of Bi2Te2Se decreases with increasing strain until the band gap reaches 0 at 9% strain, causing the system to shift from a semiconductor to a conductor. The electronic density of states is primarily determined by the 6p orbitals of Bi and 5p orbitals of Te. With regards to its mechanical properties, Bi2Te2Se satisfies the mechanical stability criterion under different strains. As the strain increases from 0% to 6%, the material becomes increasingly brittle, with its interior transitioning from metallic to covalent bonds. However, the material toughness begins to improve from 6% to 9%, with the interior transitioning from covalent to metallic bonding. The performance improvement of Bi2Te2Se varies depending on the two electric field polarization vectors along [1 0 0] and [0 0 1] directions under strain. The material shows distinct application prospects in terms of absorption coefficient, reflectivity, refractive index, and lossiness under two directions. This paper provides a theoretical reference for the future mechanical and optical applications of Bi2Te2Se.

Design of Energy Recovery Control for General Virtual Synchronous Machines Based on Various Forms of Energy Storage

The reduced inertia in the power system due to renewable energy integration introduces operation challenges in frequency stability and control. The current options for virtual inertia and frequency support are limited by the energy resources and the power electronic interface. Considering the demand on response speed and energy capacity, a general virtual synchronous machine (VSM) control based on various forms of energy storage systems (ESS) is proposed. The steady-state energy variation of energy storage is found to be proportional to the virtual damping or governor gain, while inversely proportional to the integral gain of system frequency control. It is found that the size of energy storage can be at the second time scale (for example, 6.8 p.u.·s) for VSM implementation, which is significantly smaller than the conventional hour-scale energy storage in the power system. Based on energy dynamic analysis, stability requirement, and bandwidth separation rules, an energy recovery control is designed to maintain constant state of charge (for example, 50%) while avoiding conflicts with frequency regulation. The time scale of the designed energy recovery control loop (for example, hundreds of seconds) is longer than the secondary frequency control. The effectiveness of the proposed control is verified through comprehensive case studies.

A Review of Workload Challenges in Fog Computing Environment

Users nowadays in environments with Fog computing require applications that respond quickly to their requests for everything they want to access and work quickly and require to increase in the Quality of Service (QoS) metrics such as minimum energy consumption, bandwidth efficiency, and reduction latency in a Fog network, resulting in an improvement in the system's performance, that is done by getting to know the workload on the network and how to deal with it. In this paper, the various Fog computing workloads are described, along with where each one should be executed, in addition, discuss the load-balancing techniques and strategies count as a very important issue and one of the important challenges in the Fog computing environment, that play a significant role in resource management like resource provisioning, task offloading, resource scheduling, and resource allocation this will be done based on reviewing previous research and discussing the most important concepts in it.

First-principles calculations to investigate structural, elastic, electronic, and optical properties of XSrCl3 (X = Li, Na)

The computational analysis of the compounds XSrCl3X=Li and Na is the subject of this research work. We utilized Density Functional Theory (DFT) to analyze the structural, optical, elastic, and electronic characteristics of XSrCl3(X=Li and Na) using the WIEN2K software. Birch Murnaghan curve optimization is performed to ascertain the structural details of both compounds. Using structural analysis, we learned that every compound displays a stable structural state at its optimum or ground state. The IRelast Package, which calculates elastic constants, is used to determine the elastic characteristics. Calculating these elastic characteristics reveals the compound's ductile or brittle nature, isotropy or anisotropy, and mechanical stability. Both materials are anisotropic and stable, as shown by an evaluation of elastic constants. Examining the Cauchy pressure, Poisson's ratio and Pugh ratio reveals that LiSrCl3 is a ductile compound while NaSrCl3 is brittle. We used generalized gradient approximation (GGA) to examine the electrical characteristics (Band Structure and Density of States). According to their computed band structures, these substances have wide indirect energy band gaps (R-Γ), or 3.57 eV for LiSrCl3 and 3.62 eV for NaSrCl3, which are indicative of semiconducting properties. To quantify the involvement of electronic states in the band structure, total and partial densities of states (TDOS and PDOS) are utilized. The optical characteristics of radiation up to 15 eV are estimated. Following an investigation of their optical properties, we measured these compounds' refractive indexes, absorption coefficients, and reflectivity. According to the anticipated electronic structure, the major optical spectrum peaks are listed.

One-pot synthesis of Ag-modified SrTiO3: synergistic effect of decoration and doping for highly efficient photocatalytic NOx degradation under LED

Strontium titanate is an ideal cubic-structure perovskite oxide that finds application in hydrogen production and water pollutants degradation field. However, its photocatalytic activity is limited under UV irradiation due to its wide energy band bap (∼ 3.2 eV). To overcome this limitation, different strategies, such as metal-doping or metal-decoration, have emerged. Here, Ag-modified-SrTiO3 photocatalysts were prepared for the first time by a cheap, simple and sustainable approach based on the use of Ag-enriched wastewaters. The Ag-decorated SrTiO3 synthesized by a two steps method photodegraded by nearly 77% of NOx within 3 h. The Ag-modified SrTiO3 prepared by aone-pot synthesis led to a doubly modification of the oxide: Ag+ doping and Ag nanoparticles-decoration. In this case the use of Ag-enriched wastewaters led to poor photocatactivity of the photocatalyst, probably related to the presence of other metals in the waste. However, the use of a pure Ag precursor permitted the fabrication of a highly efficient material achieving complete photodegradation of NOx, exhibiting a photoactivity 4 times higher than bare SrTiO3 and 1.3 times more active than Ag-decorated material. The photocatalytic enhancement was attributed to the combined effect of Ag-doping and Ag-decoration on SrTiO3, which contributed to a narrow band gap (2.80 eV), as well as the formation of heterojunctions that promotes the separation of photogenerated charges, respectively. This material showed good stability during recycling tests, maintaining high performances after five cycles. Eventually, active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process.

Effect of the local energy distribution of x-ray beams generated through inverse Compton scattering in dual-energy imaging applications.

X-ray sources based on the inverse Compton interaction between a laser and a relativistic electron beam are emerging as a promising compact alternative to synchrotron for the production of intense monochromatic and tunable radiation. The emission characteristics enable several innovative imaging techniques, including dual-energy K-edge subtraction (KES) imaging. The performance of these techniques is optimal in the case of perfectly monochromatic x-ray beams, and the implementation of KES was proven to be very effective with synchrotron radiation. Nonetheless, the features of inverse Compton scattering (ICS) sources make them good candidates for a more compact implementation of KES techniques. The energy and intensity distribution of the emitted radiation is related to the emission direction, which means different beam qualities in different spatial positions. In fact, as the polar angle increases, the average energy decreases, while the local energy bandwidth increases and the emission intensity decreases. The scope of this work is to describe the impact of the local energy distribution variations on KES imaging performance. By means of analytical simulations, the reconstructed signal, signal-to-noise ratio, and background contamination were evaluated as a function of the position of each detector pixel. The results show that KES imaging is possible with ICS x-ray beams, even if the image quality slightly degrades at the detector borders for a fixed collimation angle and, in general, as the beam divergence increases. Finally, an approach for the optimization of specific imaging tasks is proposed by considering the characteristics of a given source.

Sub-second pair distribution function using a broad bandwidth monochromator.

Here the use of a broad energy bandwidth monochromator, i.e. a pair of B4C/W multilayer mirrors (MLMs), is demonstrated for X-ray total scattering (TS) measurements and pair distribution function (PDF) analysis. Data are collected both on powder samples and from metal oxo clusters in aqueous solution at various concentrations. A comparison between the MLM PDFs and those obtained using a standard Si(111) double-crystal monochromator shows that the measurements yield MLM PDFs of high quality which are suitable for structure refinement. Moreover, the effects of time resolution and concentration on the quality of the resulting PDFs of the metal oxo clusters are investigated. PDFs of heptamolybdate clusters and tungsten α-Keggin clusters from X-ray TS data were obtained with a time resolution down to 3 ms and still showed a similar level of Fourier ripples to PDFs obtained from 1 s measurements. This type of measurement could thus open up faster time-resolved TS and PDF studies.

Energy Efficient Secure Key Management Scheme for Hierarchical Cluster Based WSN

Advance development in wireless sensor network (WSN) has offered tremendous applications in various fields. WSN consists of tiny sensors with unique features, capable of processing the sensed data and are resource constrained. WSN provides robust connection between objects to share information via wireless medium. Despite the significance, WSN face several issues such as more energy consumption, bandwidth constrain and security. Due to open environment and wireless medium secure data transmission within WSN is a critical issue, thus to cope with WSN applications a robust security development is required. Cluster based hierarchical network guarantees energy efficient over flat network. However existing security scheme employs high computational cryptographic functions which consumes more energy and has higher computational overhead. In this work we propose energy efficient hybrid secure key management scheme (EEHSKM) for secure communication from cluster head to base station. This scheme aims to optimize public key cryptographic steps and utilizes symmetric key cryptographic operations which extensively reduce energy consumption and ensures secure communication. The simulation results are evaluated to achieve QoS metrics.

Tom and Jerry Based Multipath Routing with Optimal K-medoids for choosing Best Clusterhead in MANET

Given the unpredictable nature of a MANET, routing has emerged as a major challenge in recent years. For effective routing in a MANET, it is necessary to establish both the route discovery and the best route selection from among many routes. The primary focus of this investigation is on finding the best path for data transmission in MANETs. In this research, we provide an efficient routing technique for minimising the time spent passing data between routers. Here, we employ a routing strategy based on Tom and Jerry Optimization (TJO) to find the best path via the MANET's routers, called Ad Hoc On-Demand Distance Vector (AODV). The AODV-TJO acronym stands for the suggested approach. This routing technique takes into account not just one but three goal functions: total number of hops. When a node or connection fails in a network, rerouting must be done. In order to prevent packet loss, the MANET employs this rerouting technique. Analyses of AODV-efficacy TJO's are conducted, and results are presented in terms of energy use, end-to-end latency, and bandwidth, as well as the proportion of living and dead nodes. Vortex Search Algorithm (VSO) and cuckoo search are compared to the AODV-TJO approach in terms of performance. Based on the findings, the AODV-TJO approach uses 580 J less energy than the Cuckoo search algorithm when used with 500 nodes.

Recent Progress of ZnO-Based Nanoparticle: Synthesizing Methods of Various Dopant and Applications

This review focus on the effect of doping rare earth metals, transition metals, noble metals, poor metals, and non-metals on ZnO nanoparticles. ZnO is a semiconductor material with an average wide energy band gap of 3.2 eV. The doping is used to improve the properties of ZnO which strongly depend on their application. The concentration of doping, the type of doping and the process using sol-gel, hydrothermal and precipitation methods are affected in modifying the ZnO lattice parameters. The transition metal widely used for photocatalysts and sensors. The doped application of ZnO nanoparticles as a semiconductor material has proven advantageous in enabling various photocatalytic, glucose biosensors, VOC detection sensors, antibacterial, biomedical, and optoelectronic spintronic, LED, NLO, and silicon solar cells. This review provided information for scientist in choosing the synthesizing methods of ZnO with desired properties and application in future.

A Model of Energy and Spectral Shape for the Internal Gravity Wave Field in the Deep Sea: The Parametric IDEMIX Model

Abstract The spectral description of the energy of oceanic internal gravity waves is generally represented by the Garrett–Munk (GM) model, a function with a power-law decrease of spectral energy in wavenumber–frequency space. Besides the slopes of these power laws, the spectrum is expressed as a function of energy and a bandwidth parameter that fixes the range of vertical modes excited in the respective state. Whereas concepts have been developed and agreed upon of what processes feed the wave spectrum and what dissipates energy, there is no explanation of what shapes the spectral distribution, i.e., how the power laws come about and what sets the bandwidth. The present study develops a parametric spectral model of energy and bandwidth from the basic underlying energy balance in terms of forcing, propagation, refraction, spectral transfer, and dissipation. The model is an extension of the IDEMIX (Internal Wave Dissipation, Energy and Mixing) models where bandwidth was taken as a constant parameter. The current version of the model is restricted to single-column mode and the slopes of the spectral power laws are fixed. A coupled system of predictive equations for energy and bandwidth (for up- and downward propagating waves) results. The equations imply that bandwidth relates to energy by a power law with an exponent given by the dynamical parameters. It agrees favorably with energy, bandwidth, and slope data from previously published fits of the GM model to Argo float observations. Numerical solutions of the coupled energy–bandwidth model in stand-alone modus are presented.

Density functional theory of Ca/F co-doped anatase TiO2

In order to understand the improved photocatalytic activity of Ca/F co-doped TiO2, the lattice parameters, energy band structures, density of states and absorption spectra of pure, Ca doped, F doped and Ca/F co-doped anatase TiO2 were calculated by first principles based on the density functional theory. It was found that the doping can result in lattice distortion of TiO2, especially the biggest lattice distortion was generated by the Ca/F co-doping. The forbidden energy band width of anatase TiO2 was broadened by Ca or F doping, while it was reduced by Ca/F co-doping. The calculated electronic density of states indicated that Ca doping provided contribution to the valence band of TiO2, and F doping resulted in the highest energy level occupied by electrons appeared in the conduction band. The energy band of TiO2 almost kept unchanged after Ca/F co-doping except the reduction of forbidden band width. Therefore, the experimentally obtained photocatalytic activity improvement of TiO2 co-doped with Ca and F may have resulted from the reduction of forbidden band width of TiO2.

Improvement of the electronic, mechanical and optical properties of cubic As-doped BN alloy for energy harvesting applications

The electronic structure, elastic and optical properties with wide energy band gap (Eg) in mixed crystal semiconductors containing As-doped BN are reported. Density functional calculations (DFT) were performed for comprehensive detection and understanding of structural, optoelectronic, and elastic properties for mixed semiconductors in the cubic phase. When applying Vegard’s law for As, BN, and mixed alloys based on BN1−xAsx, where x = 0, 0.25, 0.5, 0.75, and 1, we observed that the distortion of the lattice constants was slight to different condensations. Calculations of Eg values found that the values decreased with an increase in (x) condensation. The bulk modulus, and other elastic parameters were computed and confirmed that the alloys are mechanically stable. The calculations of dielectric Ɛ(ω), refractive index n(ω), higher absorption α(ω) peaks, and other coefficients confirm that BN1−xAsx alloys are favourable for practical photovoltaics. The results confirm that mixed semiconductors have great interest in next-generation optoelectronic devices. This work provides a route for optoelectronic applications.

In situ modification of LiMn3/4Fe1/4PO4/C cathode realized by hierarchical porous α-LiAlO2 as channel for lithium-ion batteries

In view of the lower electronic and ionic conductivity of LiMnPO4 cathode materials, we use α-LiAlO2 solid electrolyte with pore structure to compound LiMn3/4Fe1/4PO4/C solid solution on the basis of Mn site doped Fe, forming a conductive connection network between them. Using anode aluminum oxide as porous structure template, a series of LiMn3/4Fe1/4PO4/C@α-LiAlO2 nano composites are constructed by hydrothermal in-situ deposition and subsequent heat treatment. Through the first-principles calculation, it is found that the modification of α-LiAlO2 leads to an increase in the number of states near Fermi level, and the adjustment energy band width affects the electronic conductivity of LiMn3/4Fe1/4PO4 electrode. When the content of α-LiAlO2 is 6 wt%, the electronic structure of LiMn3/4Fe1/4PO4@α-LiAlO2 composite is the best and has the best performance. This material material exhibits a better specific discharge capacity, that is, 142.6, 137.7, 130.3, 117.1, 100.6, 79.2 and 68.5 mAh·g−1 at 0.5C, 2C, 4C, 8C, 10C, 15C and 20C, respectively. In addition, its DLi + is 2.02 × 10−12 cm2·s−1, which is an order of magnitude higher than that of other α-LiAlO2-containing electrodes. Hence, it is significant in cathode for lithium-ion batteries to reasonably design multi-functional hybrid materials.

Review on CeO2-Based Photocatalysts for Photocatalytic Reduction of CO2: Progresses and Perspectives

A promising approach is to transform carbon dioxide (CO2) into renewable, high value-added products with minimal environmental impact and maximum efficiency. Many problems, including energy shortages and environmental degradation, are caused by high CO2 levels, but this can help. Photocatalytic reduction methods are a promising technology for solving these problems. Cerium dioxide (CeO2) is one of the most important rare earth oxides, and cerium dioxide-based photocatalysts have gained a lot of attention in recent years due to their distinctive features, such as their tunable electronic structures and their excellent photocatalytic performances. However, the wide energy band of cerium oxide limits its utilization of light. This review provides various strategies for the modification of cerium oxide, encompassing external atom doping, heterostructure fabrication, defect fabrication, and crystal plane modulation, to improve the catalytic performance of CeO2. The fundamentals of the conversion of CeO2-based photocatalysts into high value-added products are also summarized. Finally, the challenges and prospects of CeO2-based catalysts for photocatalytic reduction of CO2 are presented.

Synthesize, construction and enhanced performance of Bi2WO6/ZnS heterojunction under visible light: Experimental and DFT study

With the simple perovskite structure, Bi2WO6 could be utilized as a modifier to overcome the low visible light response of the wide energy band photocatalyst ZnS. Flower-like Bi2WO6 was simply synthesized by hydrothermal method and Bi2WO6/ZnS heterojunction was constructed via solvothermal reaction. The results showed that ZnS nanospheres were uniformly loaded on the flower-like structure, which was well kept under low concentration loading (≤20%ωt ZnS). The degradation of MB and Rh.B under visible light was used to measure the photocatalytic activity of the photocatalysts. The degradation rates of MB and Rh.B by 20%ωt-Bi2WO6/ZnS were as high as 94.3% and 92.8%, respectively. Moreover, the degradation performance of photocatalyst still maintained 89.3% after 4 times recycling tests. The visible light absorption ability of modified ZnS was improved, and the recombination of photogenerated electrons and holes was inhibited due to the formation of heterojunction. According to the data from density functional theory calculation, the composition of the valence band and conductive band of the Bi2WO6/ZnS system has been altered. The band gap of Bi2WO6/ZnS was reduced by roughly 1.12 eV compared to that of pure ZnS, and the work function analysis were in good agreement with the experimental results. Under light stimulation, electrons were transferred from Bi2WO6 to ZnS to produce superoxide radicals which played key roles in the degradation reaction of dyes.