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Band structure and giant Stark effect in two-dimensional transition-metal dichalcogenides
摘要： We present a comprehensive study of the electronic structures of 192 configurations of 39 stable, layered, transition-metal dichalcogenides using density-functional theory. We show detailed investigations of their monolayer, bilayer, and trilayer structures’ valence-band maxima, conduction-band minima, and band gap responses to transverse electric fields. We also report the critical fields where semiconductor-to-metal phase transitions occur. Our results show that band gap engineering by applying electric fields can be an effective strategy to modulate the electronic properties of transition-metal dichalcogenides for next-generation device applications.
关键词： two-dimensional materials,band structure,giant-Stark effect,density functional theory,electric field,transition metal dichalcogenides
更新于2025-09-09 09:28:46
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Linear Optical Properties of Gold Colloid
摘要： Gold colloid was prepared by reducing HAuCl4·4H2O with Na3C6H5O7·2H2O. The morphology, size of gold nanoparticles and the optical property of colloid were characterized by transmission electron microscope and UV-Vis spectrophotometer, respectively. It shows that the gold nanoparticles are in the shape of spheres with diameters less than 8 nm, and the surface plasmon resonance absorption peak is located at about 438 nm. As the volume fraction of gold particles increases, the intensity of absorption peak strengthens. The optical property of gold colloid was analyzed by Maxwell-Garnett (MG) effective medium theory in the company of Drude dispersion model. The results show that the matrix dielectric constant is a main factor, which influences the optical property of gold colloid.
关键词： gold nanoparticle,aqueous-phase reduction,Maxwell-Garnett effective medium theory,Drude dispersion model
更新于2025-09-09 09:28:46
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Hamiltonian Monte Carlo solution of tomographic inverse problems
摘要： We present the theory for and applications of Hamiltonian Monte Carlo (HMC) solutions of linear and nonlinear tomographic problems. HMC rests on the construction of an artificial Hamiltonian system where a model is treated as a high-dimensional particle moving along a trajectory in an extended model space. Using derivatives of the forward equations, HMC is able to make long-distance moves from the current towards a new independent model, thereby promoting model independence, while maintaining high acceptance rates. Following a brief introduction to HMC using common geophysical terminology, we study linear (tomographic) problems. Though these may not be the main target of Monte Carlo methods, they provide valuable insight into the geometry and the tuning of HMC, including the design of suitable mass matrices, and the length of Hamiltonian trajectories. This is complemented by a self-contained proof of the HMC algorithm in the Appendix. A series of tomographic/imaging examples is intended to illustrate (i) different variants of HMC, such as constrained and tempered sampling, (ii) the independence of samples produced by the HMC algorithm, and (iii) the effects of tuning on the number of samples required to achieve practically useful convergence. Most importantly, we demonstrate the combination of HMC with adjoint techniques. This allows us to solve a fully nonlinear, probabilistic traveltime tomography with several thousand unknowns on a standard laptop computer, without any need for supercomputing resources.
关键词： Seismic tomography,Probability distributions,Statistical methods,Inverse theory,Numerical solutions
更新于2025-09-09 09:28:46
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Wave Propagation Concepts for Near-Future Telecommunication Systems || Light Wave Propagation and Scattering Through Particles
摘要： The study of light propagating and scattering for various particles has always been important in many practical applications, such as optical diagnostics for combustion, monitoring of atmospheric pollution, analysis of the structure and pathological changes of the biological cell, laser Doppler technology, and so on. This chapter discusses propagation and scattering through particles. The description of the solution methods, numerical results, and potential application of the light scattering by typical particles is introduced. The generalized Lorenz-Mie theory (GLMT) for solving the problem of Gaussian laser beam scattering by typical particles with regular shapes, including spherical particles, spheroidal particles, and cylindrical particles, is described. The numerical methods for the scattering of Gaussian laser beam by complex particles with arbitrarily shape and structure, as well as random discrete particles are introduced. The essential formulations of numerical methods are outlined, and the numerical results for some complex particles are also presented.
关键词： Gaussian laser beam,generalized Loren-Mie theory,light scattering,numerical method,small particles
更新于2025-09-09 09:28:46
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[IEEE 2018 International conference on computation of power, energy, Information and Communication (ICCPEIC) - Chennai, India (2018.3.28-2018.3.29)] 2018 Internat2018 International Conference on Computation of Power, Energy, Information and Communication (ICCPEIC)ional conference on computation of power, energy, Information and Communication (ICCPEIC) - Modified SEPIC Converter Based PV Inverter for Power Quality Improvement
摘要： Now a day the photovoltaic (PV) age is continuously notable, while require significantly more high-control quality. One PV generator providing to nonlinear burdens is wanted to be consolidated with a limit as an Active Power Filter (APF). In our errand, a three-arrange three-wire system, including a bare essential PV generator, modified single completed fundamental inductor converter (M-SEPIC) for high voltage change is sketched out. Furthermore, to separate greatest radiation control a most extreme power point following, calculation is utilized. Here a dc/air conditioning molding voltage source converter to go about as an Active power channel (APF), is proposed. The incite control speculation is utilized to design the PV-APF controller, which shows tried and true displays. Space vector direction (SVM) control system is used as a piece of the PV-APF controller for better execution.
关键词： instantaneous power theory,Active power filter (APF),renewable energy,photovoltaic (PV),quality of power
更新于2025-09-09 09:28:46
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Exact Camera Location Recovery by Least Unsquared Deviations
摘要： We establish exact recovery for the Least Unsquared Deviations (LUD) algorithm of "Ozye\c sil and Singer. More precisely, we show that for sufficiently many cameras with given corrupted pairwise directions, where both camera locations and pairwise directions are generated by a special probabilistic model, the LUD algorithm exactly recovers the camera locations with high probability. A similar exact recovery guarantee for camera locations was established for the ShapeFit algorithm by Hand, Lee, and Voroninski, but with typically less corruption.
关键词： robust estimation,random graph theory,structure from motion,least unsquared deviations,camera location estimation,convex recovery
更新于2025-09-09 09:28:46
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Local Electronic Structure of Molecular Heterojunctions in a Single-Layer 2D Covalent Organic Framework
摘要： The synthesis of a single-layer covalent organic framework (COF) with spatially modulated internal potentials provides new opportunities for manipulating the electronic structure of molecularly defined materials. Here, the fabrication and electronic characterization of COF-420: a single-layer porphyrin-based square-lattice COF containing a periodic array of oriented, type II electronic heterojunctions is reported. In contrast to previous donor–acceptor COFs, COF-420 is constructed from building blocks that yield identical cores upon reticulation, but that are bridged by electrically asymmetric linkers supporting oriented electronic dipoles. Scanning tunneling spectroscopy reveals staggered gap (type II) band alignment between adjacent molecular cores in COF-420, in agreement with first-principles calculations. Hirshfeld charge analysis indicates that dipole fields from oriented imine linkages within COF-420 are the main cause of the staggered electronic structure in this square grid of atomically–precise heterojunctions.
关键词： type II heterojunctions,covalent organic frameworks,density functional theory,scanning tunneling microscopy and spectroscopy,electronic structure
更新于2025-09-09 09:28:46
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Bandgap Tunability in a One-Dimensional System
摘要： The ability to tune the gaps of direct bandgap materials has tremendous potential for applications in the ?elds of LEDs and solar cells. However, lack of reproducibility of bandgaps due to quantum con?nement observed in experiments on reduced dimensional materials, severely affects tunability of their bandgaps. In this article, we report broad theoretical investigations of direct bandgap one-dimensional functionalized isomeric system using their periodic potential pro?le, where bandgap tunability is demonstrated simply by modifying the potential pro?le by changing the position of the functional group in a periodic supercell. We found that bandgap in one-dimensional isomeric systems having the same functional group depends upon the width and depth of the deepest potential well at global minimum and derived correlations are veri?ed for known synthetic as well as natural polymers (biological and organic), and also for other one-dimensional direct bandgap systems. This insight would greatly help experimentalists in designing new isomeric systems with different bandgap values for polymers and one-dimensional inorganic systems for possible applications in LEDs and solar cells.
关键词： one-dimensional systems,polymers,nanoribbons,density functional theory,bandgap
更新于2025-09-09 09:28:46
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Implications of spectral-hole burning on the manipulation of spatial Goos–H?nchen shift in an atomic cell
摘要： We present a new scheme to report on Goos–H?nchen (GH) shift experienced by the Gaussian light beam incident at the plane optical interface filled with four-level sodium atomic medium in the spectral-hole burning region with and without Doppler broadening effect. Theoretical atomic density-matrix formalism is employed to obtain the susceptibility of atomic medium while the stationary-phase-theory is used to compute the GH shift in the reflected and transmitted probe beams subjected to control fields. A steep normal slope of dispersion is observed with a maximum and zero probability of transmission and reflection coefficients, respectively, at the regions of the spectral holes burning. In the normal dispersion spectrum at the region of spectral-hole burning, positive and negative GH shift is observed, respectively, in the transmitted and reflected light beams. However, at anomalous dispersive regions negative GH shift in the transmission beam and positive GH shift in the reflection beam is observed. The reflection and transmission coefficients as well as the spatial GH shift are the functions of probe detuning, collective phase of control fields and inverse Doppler broadening effect in the spectral-hole burning region. The study is expected to be useful for optoelectronic devices and optical-clocking applications.
关键词： Doppler broadening medium,Density-matrix formalism,Spectral hole burning,Spatial Goos–H?nchen shift,Stationary-phase-theory
更新于2025-09-09 09:28:46
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Synthesis, Structure, and Properties of the Layered Oxide Chalcogenides Sr <sub/>2</sub> CuO <sub/>2</sub> Cu <sub/>2</sub> S <sub/>2</sub> and Sr <sub/>2</sub> CuO <sub/>2</sub> Cu <sub/>2</sub> Se <sub/>2</sub>
摘要： The structures of two new oxide chalcogenide phases, Sr2CuO2Cu2S2 and Sr2CuO2Cu2Se2, are reported, both of which contain infinite CuO2 planes containing Cu2+ and which have Cu+ ions in the sulfide or selenide layers. Powder neutron diffraction measurements show that Sr2CuO2Cu2Se2 exhibits long-range magnetic ordering with a magnetic structure based on antiferromagnetic interactions between nearest-neighbor Cu2+ ions, leading to a √2a × √2a × 2c expansion of the nuclear cell. The ordered moment of 0.39(6) μB on the Cu2+ ions at 1.7 K is consistent with the value predicted by density functional theory calculations. The compounds are structurally related to the cuprate superconductors and may also be considered as analogues of the parent phases of this class of superconductor such as Sr2CuO2Cl2 or La2CuO4. In the present case, however, the top of the chalcogenide-based valence band is very close to the vacant Cu2+ 3d states of the conduction band, leading to relatively high measured conductivity.
关键词： oxide chalcogenides,Sr2CuO2Cu2Se2,Sr2CuO2Cu2S2,density functional theory,cuprate superconductors,magnetic ordering
更新于2025-09-09 09:28:46