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- 实验方案
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Optimizing the conductance switching performance in photoswitchable dimethyldihydropyrene/cyclophanediene single-molecule junctions
摘要： Designing molecular switches with high stability and performance is still a great challenge in the field of molecular electronics. For this aim, key factors influencing the charge transport properties of molecular devices require to be carefully addressed. Here, by using the nonequilibrium Green’s function method in combination with the density functional theory, effect of bridging manner (i.e., linkage sites) for dimethyldihydropyrene (DHP)/cyclophanediene (CPD) photoswitchable molecule sandwiched between two Au(111) electrodes has been theoretically investigated. The computational results show that the fully conjugated DHP is more conductive than the less conjugated CPD, manifesting an evident switching effect. It is also found that the ON/OFF switching performance of DHP/CPD is dramatically modulated by the bridging manner. Further analysis attributes the switching feature to the different alignments of conducting HOMO with the Fermi energy for DHP and CPD. And it also reveals that local bond contributions to the electron transmission pathway are closely related to both the conjugation characteristics and bridging manner of the core molecule. This work suggests that the bridging manner of core molecule in single-molecule junction plays an essential role in determining the switching performance and should be carefully addressed in future design of molecular switches.
关键词： Single-molecule switch,Density functional theory,Nonequilibrium Green’s function method
更新于2025-09-23 15:23:52
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Non-Equilibrium Green's Function based Circuit Models for Coherent Spin Devices
摘要： With recent developments in spintronics, it is now possible to envision 'spin-driven' devices with magnets and interconnects that require a new class of transport models using generalized Fermi functions and currents, each with four components: one for charge and three for spin. The corresponding impedance elements are not pure numbers but 4 × 4 matrices. Starting from the Non-Equilibrium Green's Function (NEGF) formalism in the elastic, phase-coherent transport regime, we develop spin generalized Landauer-Büttiker formulas involving such 4 × 4 conductances, for multi-terminal devices in the presence of Normal-Metal (NM) leads. In addition to usual 'terminal' conductances describing currents at the contacts, we provide 'spin-transfer torque' conductances describing the spin currents absorbed by ferromagnetic (FM) regions inside the conductor, specifying both of these currents in terms of Fermi functions at the terminals. We derive universal sum rules and reciprocity relations that would be obeyed by such matrix conductances. Finally, we apply our formulation to two example Hamiltonians describing the Rashba and the Hanle effect in 2D. Our results allows the use of pure quantum transport models as building blocks in constructing circuit models for complex spintronic and nano-magnetic structures and devices for simulation in SPICE-like simulators.
关键词： Rashba effect,spintronics,Landauer-Büttiker formula,spin-transfer torque,Non-Equilibrium Green's Function,Hanle effect,SPICE simulation
更新于2025-09-23 15:23:52
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Transport properties of doped zigzag graphene nanoribbons
摘要： Numerous studies on materials have driven the development of modern nanoelectronic devices. And research also shown that the integrated circuits have entered the era of the nanoelectronic scales from the scale of microelectronics. But the limitations of copper as a traditional connection, such as the resistivity increases a lot, further causing a lot of heat in the interconnect, have been highlighted. Therefore, we need new materials as the substitution of copper. The metallic properties exhibited by the zigzag graphene nanoribbons (ZGNRs) can be controlled by the edge states, doping and different widths of the nanoribbons. In this paper, we applied simulation to dope copper atom chains on ZGNRs. We found an energetic phenomenon that after doping the nanoribbons conductivity have increased significantly than the original. In addition, the transmission channels are mainly concentrated near the doping position, and the width used for transmission is greatly reduced after doping. It is expected to be used as an inter-connect application in nano-integrated circuits in the future.
关键词： Density functional theory,Interconnect,Electronic transport property,Non-equilibrium Green's function,Zigzag graphene nanoribbons,Doping
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - The Impact of Dopant Diffusion on Random Dopant Fluctuation in Si Nanowire FETs: A Quantum Transport Study
摘要： In this work, we perform statistical quantum transport simulations with 3×3 nm2 Si nanowire (NW) field-effect transistors (FETs) to investigate the impact of dopant diffusion on random dopant fluctuation. First, we use an effective mass Hamiltonian for the transport where the confinement and transport effective masses are extracted from the tight-binding band structure calculations. The dopant diffusion along the transport direction from the source/drain regions to the channel region is modeled by the Gaussian doping profile. To generate random discrete dopants, we adopt a rejection scheme considering the 3-dimensional atomic arrangement of the NW structures. Our statistical simulation results show that the diffused dopants into the channel region cause large variability problems in Si NW FETs.
关键词： non-equilibrium Green's function,tight-binding,dopant diffusion,random discrete dopants,silicon nanowire
更新于2025-09-23 15:22:29
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Superior Sensing Properties of Black Phosphorus as Gas Sensors: A Case Study on the Volatile Organic Compounds
摘要： The unique structure and prominent properties of black phosphorus (BP) and its monolayer and multilayers in device applications have attracted significant attention to this elemental 2D material. In this study, a comprehensive evaluation of the candidacy of monolayer BP as a channel material for high-performance volatile organic compound (VOC) sensors is conducted combining first-principles density functional theory calculations and non-equilibrium Green’s function formalism. The adsorption configurations and energetics of several typical VOCs (ethanol, propionaldehyde, acetone, toluene, and hexane) on monolayer BP are examined and it is demonstrated that VOCs generally exhibit stronger interaction with monolayer BP than with the widely studied monolayer MoS2, indicative of monolayer BP potentially being a more sensitive VOC sensor. Monolayer BP is shown to exhibit highly anisotropic transport behaviors, whereas the absolute modification of current–voltage responses due to VOCs is found to show a trend that is direction independent. Moreover, the adsorption of VOCs on monolayer BP is strong enough to resist thermal disturbance, yet allows fast recovery time. The results suggest that BP is a compelling and feasible candidate for sensing applications of VOCs.
关键词： density functional theory calculations,gas sensors,black phosphorus,volatile organic compounds,non-equilibrium Green’s function formalism
更新于2025-09-23 15:22:29
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Love-type waves in a piezoelectric-viscoelastic bimaterial composite structure due to an impulsive point source
摘要： The analysis of wave propagation phenomenon piezoelectric-viscoelastic composites still remains an unexplored field of research. The usage of a passive polymer (Epoxy) with active piezoelectric ceramic causes viscoelasticity in the piezoelectric material which results into a piezoelectric-viscoelastic composite. The present study aims to analyze the propagation behavior of Love-type wave in an exponentially graded piezoelectric-viscoelastic material (EGPVM) stratum lying over a functionally graded piezoelectric-viscoelastic material (FGPVM) substrate due to an impulsive point source at its interfacial surface. The electro-visco-mechanical field equations are laid down for the piezoelectric-viscoelastic medium.The analytical solution procedure involves the use of suitable Green’s function and admissible boundary conditions. The established frequency equation is in complex form; of which the real expression imparts the frequency curve and imaginary expression gives the attenuation curve of Love-type wave. To depict the results numerically, two distinct piezoelectric-viscoelastic materials (Epoxy-BNKLBTand Epoxy-KNLNTSceramics) for EGPVM stratum and FGPVM substrate are taken into account.The phase velocity profile and attenuation coefficient profile of Love-type wave is portrayed graphically. Diagnostic results are simulated numerically which forefronts the effect of distinct parameters. The study manifests the impact of the material medium parameters, viz. piezoelectric constants, dielectric constants, piezoelectric loss moduli, dielectric loss moduli, exponential gradient parameter and magnifying gradient parameters on the phase velocity and attenuation coefficient of Love-type wave. For sake of validation, the obtained results are matched with the classical one, as a special case of the problem. The outcomes of the study may find its worth in better and optimum design of surface acoustic wave devices and Love wave sensors, keeping efficiency at its premium.
关键词： Piezoelectric-viscoelastic,damping equation,frequency equation,point source,Green’s function,attenuation coefficient.
更新于2025-09-23 15:22:29
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Local photo-excitation of shift current in noncentrosymmetric systems
摘要： Photocurrent in solids is an important phenomenon with many applications including the solar cells. In conventional photoconductors, the electrons and holes created by light irradiation are separated by the external electric field, resulting in a current flowing into electrodes. Shift current in noncentrosymmetric systems is distinct from this conventional photocurrent in the sense that no external electric field is needed and, more remarkably, is driven by the Berry phase inherent to the Bloch wavefunction. It is analogous to the polarization current in the ground state but is a dc current continuously supported by the nonequilibrium steady state under the pumping by light. Here we show theoretically, by employing Keldysh–Floquet formalism applied to a simple one-dimensional model, that the local photo excitation can induce the shift current which is independent of the position and width of the excited region and also the length of the system. This feature is in stark contrast to the conventional photocurrent, which is suppressed when the sample is excited locally at the middle and increases towards the electrodes. This finding reveals the unconventional nature of shift current and will pave a way to design a highly efficient photovoltaic effect in solids.
关键词： nonequilibrium Green’s function method,shift current,photovoltaic effect
更新于2025-09-23 15:21:21
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[IEEE 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Sao Paulo, Brazil (2019.10.7-2019.10.9)] 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Spectral Analysis of a Nanodipole Array above the Surface Impedance of Graphene by Greena??s Function
摘要： In this paper, we present a spectral analysis of a nanodipole array above a graphene layer by the Periodic Green’s Function (PGF) method. The graphene layer deposited on a dielectric substrate is modeled as a surface impedance with conductivity described by the Kubo model. The Green’s function is obtained by the complex two-dimensional Fourier series transform, with impedance condition at the interface between the dielectric media. We performed a parametric analysis of the in?uence of chemical potential on the absorbance and the electromagnetic ?elds in the spectral domain. For the modeling used, the dispersion characteristic of graphene is also veri?ed. From the spectral analysis we investigated the emergence of the Surface Plasmon Polariton (SPP) pole in the spectral representation. Finally, we compared the model based on impedance condition with a formulation that considers graphene with a ?nite thickness.
关键词： Spectral Analysis,Plasmonics,Green’s Function,Graphene
更新于2025-09-23 15:21:01
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Efficient Characterization of Topological Photonics Using the Broadband Greena??s Function
摘要： A novel method is developed in this paper to characterize the band diagram and modal ?elds of gyromagnetic photonic crystals that support topolgoical one-way edge states. We exploy an integral equation based method that utilizes the broadband Green’s function as the kernel. The broadband Green’s function is a hybrid representation of the periodic lattice Green’s function that includes an imaginary wavenumber component represented in exponentially decaying spatial series and a reminder in fast converging Floquet plane wave expansions. Special boundary conditions govern the ?elds across the interface of the gyromagnetic scatterers, leading to surface integral equations (SIEs) that involve three components including the pilot ?eld, its normal derivative and its tangential derivative. To reduce the independent number of unknowns, roof-top basis functions and the Garlerkin’s method are used to discretize the SIEs into matrix equations. The broadband Green’s function allows converting the discretized SIEs into a linear eigenvalue problem of a small size. The eigenvalues and eigenvectors of the linear eigenvalue problem are directly related to the band solutions and modal ?elds of the photonic crystal. The proposed approach is an e?ective method to characterize wave interactions with periodic scatterers using integral equations. The solutions of the presented approach are compared against Comsol simulations for various cases to show its accuracy and e?ciency.
关键词： topological photonics,surface integral equations,broadband Green’s function,linear eigenvalue problem,gyromagnetic photonic crystals
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Lviv, Ukraine (2019.7.2-2019.7.6)] 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Calculation of Spectral Greena??s Function and Its Asymptotical Behavior for Sheet Electric Current in Two-Layer Dielectric Waveguide
摘要： Structures with patches placed on the interfaces in a two-layered dielectric waveguide are promising to be used in different applications at THz waves. To realize the method of moments (MoM) solution in the spectral domain spectral Green’s functions (GFs) for sheet electric currents on the interfaces of the two-layer dielectric cylindrical waveguide are needed. This paper presents the way to enhance the MoM solution efficiency by extracting an asymptotic behavior of the spectral GF which depends on two variables: the propagation constant and the azimuth index. Here asymptotic spectral GFs are constructed and calculated when electrical sheet current is placed on different interfaces.
关键词： two-layered cylindrical dielectric waveguide,spectral Green’s function,cylindrically conformal antenna
更新于2025-09-23 15:21:01