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Many-body States Description of Single-molecule Electroluminescence Driven by Scanning Tunneling Microscope
摘要： Electron transport and optical properties of a single molecule in contact with conductive materials have attracted considerable attention owing to their scientific importance and potential applications. With recent progresses of experimental techniques, especially by the virtue of scanning tunneling microscope (STM)-induced light emission, where the tunneling current of the STM is used as an atomic-scale source for induction of light emission from a single molecule, it becomes possible to investigate single-molecule properties at sub-nanometer spacial resolution. Despite extensive experimental studies, the microscopic mechanism of electronic excitation of a single molecule in STM-induced light emission is yet to be clarified. Here we present a formulation of single-molecule electroluminescence driven by electron transfer between a molecule and metal electrodes based on a many-body state representation of the molecule. The effects of intra-molecular Coulomb interaction on conductance and luminescence spectra are investigated using the nonequilibrium Hubbard Green's function technique combined with first-principles calculations. We compare simulation results with experimental data and find that the intra-molecular Coulomb interaction is crucial for reproducing recent experiments for a single phthalocyanine molecule. The developed theory provides a unified description of both electron-transport and optical properties of a single molecule in contact with metal electrodes driven out of equilibrium, and thereby it contributes to a microscopic understanding of optoelectronic conversion in single molecules on solid surfaces and in nanometer-scale junctions.
关键词： Single molecule luminescence,exciton formation,nonequilibrium Hubbard Green's function technique,time-dependent density functional theory (TDDFT),scanning tunneling microscope-induced light emission,Vibronic interaction
更新于2025-09-19 17:15:36
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Theoretical and experimental studies on DC conductivity and temperature-dependent AC conductivity of poly(butyl methacrylate)/Nd-TiO <sub/>2</sub> nanocomposites
摘要： Electrically conductive nanocomposite system based on poly(butyl methacrylate) (PBMA) with different contents of neodymium-doped titanium dioxide (Nd-TiO2) was prepared by in situ free radical polymerization method. The effect of Nd-TiO2 on the morphology and structural properties of the composites was carried out by scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). The temperature-dependent AC conductivity and DC electrical conductivity of PBMA/Nd-TiO2 nanocomposites were studied with respect to the different volume fraction of Nd-TiO2 nanoparticles. SEM and XRD patterns revealed the uniform dispersion and structural regularity of nanoparticles in the polymer matrix. The AC conductivity of PBMA and its composites were found to be increased with an increase in temperatures and frequencies. The activation energy and exponential factor were analyzed from AC conductivity and both results indicate the hopping conduction mechanism present in PBMA/Nd-TiO2 nanocomposite, which is responsible for the variation of conductivity with temperature also. The DC conductivity of nanocomposites was higher than pure PBMA and the conductivity increases with increase in the concentration of Nd-TiO2 nanoparticles. Experimental and theoretical investigations based on McCullough, Bueche, Scarisbrick, and Mamunya modeling were carried out to observe the DC conductivity differences induced by the addition of Nd-TiO2 nanoparticles in PBMA matrix. Among the various modeling studied here, Mamunya model shows better agreement with the experimental conductivity.
关键词： Poly(n-butyl methacrylate),DC conductivity,conductivity modeling,temperature-dependent AC conductivity
更新于2025-09-19 17:15:36
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Amphipathic carbon dots with solvent-dependent optical properties and sensing application
摘要： Carbon dots (CDs) have been regarded as novel heavy-metal-free fluorescent materials because of their prominent optical features. In this work, one type of amphipathic CDs is prepared by facile one-step solvothermal treatment of p-Phenylenediamine. The obtained CDs own numerous surface function groups which endow them prominent dispersibility in different solvents. Absorption, steady-state and time-resolved spectroscopy have been adopted to investigate the mutual influence between the surface groups and different solvent molecules on the optical properties of the CDs. Strong solvatochromic behavior with tunable emission from blue to green and strict excitation-independent emission characteristic can be observed when the as-prepared CDs are dissolved in different solvents, suggesting their feasible sensing applications as an alternative of solvatochromic dye molecules. Furthermore, highly selective detection of Cu2+ ions using the as-synthesized CDs as sensing probes is achieved. It is expected that the investigated CDs with solvent-dependent optical properties as well as selective Cu2+ detection may have broad application prospects in bioimaging and biodetecting.
关键词： Cu2+ detection,Optical properties,Solvent-dependent,Carbon dots
更新于2025-09-19 17:15:36
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Two-Electron Interference in Strong-Field Ionization of He by a Short Intense Extreme Ultraviolet Laser Pulse
摘要： Double ionization of helium by a single intense (above 1018 W=cm2) linearly polarized extreme ultraviolet laser pulse is studied by numerically solving the full-dimensional time-dependent Schr?dinger equation. For the laser intensities well beyond the perturbative limit, novel gridlike interference fringes are found in the correlated energy spectrum of the two photoelectrons. The interference can be traced to the multitude of two-electron wave packets emitted at different ionization times. A semianalytical model for the dressed two-photon double ionization is shown to qualitatively account for the interference patterns in the joint energy spectrum. Similar signatures of interferences between transient induced time-delayed ionization bursts are expected for other atomic and molecular multielectron systems.
关键词： strong-field ionization,two-electron interference,time-dependent Schr?dinger equation,double ionization,extreme ultraviolet laser pulse
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Computed tomography dataset analysis for stereotaxic neurosurgery navigation
摘要： First-ever 28 nm embedded split-gate MONOS (SG-MONOS) ?ash macros have been developed to increase memory capacity embedded in micro controller units and to improve performance over wide junction temperature range from C to 170 C as demanded strongly in automotive uses. Much attention has been paid to the degradation of the reliability characteristics along with the process shrinkage. Temperature-adjusted word-line overdrive scheme improves random read access frequency by 15% and realizes both of 6.4 GB/s read throughput by 200 MHz no-wait random access of code ?ash macros and more than ten times longer TDDB lifetime of WL drivers. Temperature-adaptive step pulse erase control (TASPEC) improves the TDDB lifetime of dielectric ?lms between metal interconnect layers by three times. TASPEC is particularly useful for a data ?ash macro with one million rewrite cycles. Source-side injection (SSI) program with negative back-bias voltage achieves 63% reduction of program pulse time and, consequently, realizes 2.0 MB/s write throughput of code ?ash macros. A spread spectrum clock generation and a clock phase shift technique are introduced for charge pump clock generation in order to suppress EMI noise due to high write throughput of code ?ash macros, and peak power of EMI noise is reduced by 19 dB.
关键词： high-temperature operation,time dependent dielectric breakdown,Automotive application,high reliability,spread spectrum clock generation,word-line over-drive,split-gate MONOS(SG-MONOS),embedded ?ash memory,Fast random read operation
更新于2025-09-19 17:13:59
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Study on a Multi-channel Switchable and Environment Self-adaptive Ultrasonic Sensor in an Erbium-doped Fiber Ring Laser
摘要： The usefulness of the information contained in biomedical data relies heavily on the reliability and accuracy of the methods used for its extraction. The conventional assumptions of stationarity and autonomicity break down in the case of living systems because they are thermodynamically open, and thus constantly interacting with their environments. This leads to an inherent time-variability and results in highly nonlinear, time-dependent dynamics. The aim of signal analysis usually is to gain insight into the behavior of the system from which the signal originated. Here, a range of signal analysis methods is presented and applied to extract information about time-varying oscillatory modes and their interactions. Methods are discussed for the characterization of signals and their underlying nonautonomous dynamics, including time-frequency analysis, decomposition, coherence analysis and dynamical Bayesian inference to study interactions and coupling functions. They are illustrated by being applied to cardiovascular and EEG data. The recent introduction of chronotaxic systems provides a theoretical framework within which dynamical systems can have amplitudes and frequencies which are time-varying, yet remain stable, matching well the characteristics of life. We demonstrate that, when applied in the context of chronotaxic systems, the methods presented facilitate the accurate extraction of the system dynamics over many scales of time and space.
关键词： phase coherence,coupling function,Biomedical signal analysis,dynamical Bayesian inference,wavelet bispectrum,cardiovascular system,time-frequency analysis,brain dynamics,time-dependent dynamics
更新于2025-09-19 17:13:59
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A new approach to the schrodinger equation with position-dependent mass and its implications in quantum dots and semiconductors
摘要： In this study, we introduce a new approach to construct the Schr?dinger equation with position-dependent mass characterized by an emerging particle’s effective mass, in perfect analogy with the problems involving a position-dependent mass particle in semiconductor heterostructures. We have discussed several of its properties and some of its implications in quantum dots and semiconductors. It was observed that the PDM approach affects only semiconductors with large interatomic scaling such as non-crystalline semiconductors and its effect on conventional semiconductors is insignificant.
关键词： spatial transformation,quantum dots,Position-dependent mass,interatomic scaling
更新于2025-09-19 17:13:59
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Etch Characteristics of Si and TiO<sub>2</sub> Nanostructures Using Pulse Biased Inductively Coupled Plasmas
摘要： The etch characteristics of Si and TiO2 nanostructures for optical devices were investigated using pulse biased inductively coupled plasmas (ICP) with SF6/C4F8/Ar and BCl3/Ar, respectively, and the results were compared with those etched using continuous wave (CW) biased ICP. By using pulse biasing compared to CW biasing in the etching in the line/pillar nanostructures of various aspect ratios, the reduction of aspect ratio dependent etching (ARDE), therefore, uniform etch depths for nanostructures with different pattern widths, and the improvement of the etch profiles without notching were obtained not only for silicon nanostructures but also for TiO2 nanostructures. It is investigated that the improvement of etch profiles and less ARDE effect by using pulse biasing are related to the decreased surface charging by neutralization of the surface and the improved radical adsorption (or etch byproduct removal) on the etched surfaces during the pulse-off period for the pulse biasing compared to CW biasing.
关键词： TiO2 nanostructure,Aspect ratio dependent etch (ARDE),Pulsed plasma etching,Etch profile,Si nanostructure
更新于2025-09-19 17:13:59
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - High Power Terahertz Source Based on Planar Antenna Integrated Vacuum Photodiode
摘要： The usefulness of the information contained in biomedical data relies heavily on the reliability and accuracy of the methods used for its extraction. The conventional assumptions of stationarity and autonomicity break down in the case of living systems because they are thermodynamically open, and thus constantly interacting with their environments. This leads to an inherent time-variability and results in highly nonlinear, time-dependent dynamics. The aim of signal analysis usually is to gain insight into the behavior of the system from which the signal originated. Here, a range of signal analysis methods is presented and applied to extract information about time-varying oscillatory modes and their interactions. Methods are discussed for the characterization of signals and their underlying nonautonomous dynamics, including time-frequency analysis, decomposition, coherence analysis and dynamical Bayesian inference to study interactions and coupling functions. They are illustrated by being applied to cardiovascular and EEG data. The recent introduction of chronotaxic systems provides a theoretical framework within which dynamical systems can have amplitudes and frequencies which are time-varying, yet remain stable, matching well the characteristics of life. We demonstrate that, when applied in the context of chronotaxic systems, the methods presented facilitate the accurate extraction of the system dynamics over many scales of time and space.
关键词： phase coherence,coupling function,Biomedical signal analysis,dynamical Bayesian inference,wavelet bispectrum,cardiovascular system,time-frequency analysis,brain dynamics,time-dependent dynamics
更新于2025-09-19 17:13:59
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Soft Lattice and Defect Covalency Rationalize Tolerance of ?2a??CsPbI3 Perovskite Solar Cells to Native Defects
摘要： Although all-inorganic lead halide perovskite solar cells have shown tremendous improvement over the past few years, they are still inferior to the hybrid organic-inorganic perovskites in the solar power conversion efficiency. Recently, a conceptually new β-CsPbI3 perovskite has demonstrated an impressive 18.4% efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non-adiabatic molecular dynamics to show that native point defects in β-CsPbI3 are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. Moreover, formation of new covalently bound species in the presence of defects slows down the recombination. These results indicate that halide perovskites do not follow the simple models used to explain defect-mediated charge recombination in the conventional semiconductors. The strong tolerance of electron-hole recombination against defects arises due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and allows only low-frequency vibrations to couple to the electronic subsystem. Both factors decrease significantly the non-adiabatic coupling and slow down the dissipation of electronic energy to heat. We suggest that a halide-rich synthesis environment may further improve the efficiency, and propose that strong defect tolerance is general to metal halide perovskites because they exhibit much lower bulk moduli compared to the conventional semiconductors used in photovoltaic, photocatalytic, electrocatalytic, lasing, light-emitting, detecting and other opto-electronic devices.
关键词： Electron-phonon coupling,Nonradiative recombination,All-inorganic perovskites,Time-dependent density functional theory,Defects
更新于2025-09-19 17:13:59