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Many-electron character of two-photon above-threshold ionization of Ar
摘要： The absolute generalized cross sections and angular distribution parameters of photoelectrons for the two-photon above-threshold 3p ionization of Ar were calculated in the exciting photon energy range from 15.76 to 36 eV. The correlation function technique developed earlier was extended for the case when an intermediate-state function is of a continuum-type. We show that two-photon ionization of Ar near the 3p4 threshold to a large extent is determined by the (3p (cid:2)(cid:2)(cid:3) εd )2 two-photon absorption via the giant resonance. This many-electron correlation causes (i) an increase of the photoionization cross sections by more than a factor of 3; and (ii) the appearance of resonances in the exciting-photon energy range of the doubly excited states. The predictions are supported by a good agreement between length and velocity results obtained after taking into account the higher-order perturbation theory corrections.
关键词： angular distribution,two-photon ionization,above-threshold ionization,many-electron correlations,argon,generalized cross sections
更新于2025-09-23 15:23:52
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Stark Effect and Environment-Induced Modulation of Emission in Single Halide Perovskite Nanocrystals
摘要： Organic-inorganic halide perovskites have emerged as promising materials for next generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working opto-electronic devices external factors, such as the effects of conducting environment and of the applied electric field on exciton generation and photon emission have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr3 dispersed polyvinyl carbazole, a hole-conductor, and in polymethyl methacrylate, an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a non-linear spectral-shift of the PL maxima, a combination of linear and quadratic Stark effect caused by environment-induced polarity and field-related polarizability. The environment and electric field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively-charged excitons.
关键词： ionization,halide perovskite nanocrystals,single-particle spectroscopy,Stark effect,blinking
更新于2025-09-23 15:23:52
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Two- and Three-Photon Partial Photoionization Cross Sections of Li+, Ne8+ and Ar16+ under XUV Radiation
摘要： In this work, we present the photon energy dependence of the two- and three-photon cross sections of the two-electron Li+, Ne8+ and Ar16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on the lowest-order (non-vanishing) perturbation theory for the electric field, while the calculations are made with the use of an ab initio configuration interaction method. The ionization cross section is dominated by pronounced single photon resonances in addition to peaks associated with doubly excited resonances. In the case of two-photon ionization, and in the non-resonant part of the cross section, we find that the 1D ionization channel overwhelms the 1S one. We also observe that, as one moves from the lowest atomic number ion, namely Li+, to the highest atomic number ion, namely Ar16+, the cross sections generally decrease.
关键词： free-electron laser,X-ray radiation,cross sections,lowest-order perturbation theory,multiphoton ionization
更新于2025-09-23 15:23:52
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Design and Analysis of Gate Engineered Dual Material Gate Double Gate Impact Ionization Metal Oxide Semiconductor
摘要： In this exposition, we have proposed the Dual Material Gate Double Gate Impact Ionization Metal Oxide Semiconductor (DMG DG IMOS) device with a gate engineered technique of Gate Stacking which is ordinarily used in MOSFET for performance augmentation. This paper compares the performance of four DG IMOS based devices i.e. Single Material Gate Double Gate IMOS (SMG DG IMOS), SMG Gate Stacked DG IMOS (SMG GS DG IMOS), DMG DG IMOS and DMG Gate stacked DG IMOS (DMG GS DG IMOS). The performance of all the devices has been investigated using 2-D simulations. The device structures of gate stacked devices have been developed with two gate oxides namely SiO2 and HfO2 and remaining parameters have been taken alike for all four devices. The doping concentration of source and drain regions for all four devices has been taken as 1020 cm?3 and the doping concentration of the intrinsic region has been taken as 1015 cm?3. The Gate Stacked devices showed better analog outcomes as compared to the other devices. The analog parameters evaluated include transconductance (gm), total gate capacitance (Cgg) and unity gain frequency (fT). The proposed design, DMG GS DG IMOS has been then analyzed for different channel lengths and dielectrics of gate oxide materials to optimize the gate engineered design for various applications.
关键词： Impact ionization MOS (IMOS),Analog and RF parameters,Dual Material Gate Double Gate IMOS,Gate engineering and gate stack
更新于2025-09-23 15:23:52
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Electronic Structure of Chlorophyll a Solution Investigated by Photoelectron Yield Spectroscopy
摘要： Various bio-related processes are driven by electron transfer reactions. Therefore the electronic structures of bio-molecules in their living environment are keys of their functionalities. One significant example photosynthesis which has attracted much attention due to urgent necessity of clean energy source. In this study, we carried out photoelectron yield spectroscopy (PYS) measurements to demonstrate the electronic structures of oligomerizedChl-a molecules, which is known as an essential reaction center of the photosystem in general green plants, under the atmospheric environment. The ionization energies of the Chl-a aggregates are successfully derived.
关键词： Photoelectron Yield Spectroscopy,Polarization energy,Light harvesting antenna,Photosynthesis,Photosystem,Electronic structure,Ionization energy,Reaction center,Chlorophyll a
更新于2025-09-23 15:23:52
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Negative charge enhancement of near-surface nitrogen vacancy centers by multicolor excitation
摘要： Nitrogen vacancy (NV) centers in diamond have been identified over the past few years as promising systems for a variety of applications, ranging from quantum information science to magnetic sensing. This relies on the unique optical and spin properties of the negatively charged NV. Many of these applications require shallow NV centers, i.e., NVs that are close (a few nm) to the diamond surface. In recent years there has been increasing interest in understanding the spin and charge dynamics of NV centers under various illumination conditions, specifically under infrared (IR) excitation, which has been demonstrated to have significant impact on the NV centers’ emission and charge state. Nevertheless, a full understanding of all experimental data is still lacking, with further complications arising from potential differences between the photodynamics of bulk and shallow NVs. Here we suggest a generalized quantitative model for NV center spin- and charge-state dynamics under both green and IR excitation. We experimentally extract the relevant transition rates, providing a comprehensive model which reconciles all existing experimental results in the literature, except for highly nonlinear regimes. Moreover, we identify key differences between the photodynamics of bulk and shallow NVs, and use them to significantly enhance the initialization fidelity of shallow NVs to the useful negatively charged state.
关键词： nitrogen vacancy centers,recombination,shallow NVs,bulk NVs,photodynamics,green excitation,ionization,charge state,IR excitation,diamond
更新于2025-09-23 15:23:52
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Development and characterization of air kerma cavity standard
摘要： Ionization chambers are the most common detectors for precise measurements such as these required in radiation protection and radiotherapy. This paper presents the design, development and characterization of a new graphite–walled cavity ionization chamber used as a primary standard for air kerma rate for 137Cs and 60Co gamma radiation of the Central Office of Measures (GUM). The paper describes particularly methods for a cavity volume determination and the cavity volume relation to an electric field. The various correction factors to be applied to the primary standards and their determination by experimental and Monte Carlo methods are discussed. Re–evaluation of the standard according to the recommendations of ICRU90 Report for the new primary standard is presented. A typical uncertainty budget for the graphite-walled cavity ionization chamber as a primary standard for air kerma rate for gamma radiation is presented and results of internal comparisons between standards are summarized and discussed.
关键词： ionization chamber,air kerma cavity standard,Monte Carlo simulation,gamma radiation
更新于2025-09-23 15:23:52
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Theoretical and experimental insights into the effects of oxygen-containing species within CNTs towards triiodide reduction
摘要： Heteroatom-doped micro/nano-structured carbon materials feature unique superiorities for replacement of noble metal Pt counter electrode (CE) in dye-sensitized solar cells. Nevertheless, the effects of oxygen-containing species on/within carbon matrix on its electrocatalytic activity are seldomly considered and concerned, which will be hindered by a trade off between oxygen defects and conductivity. Herein, we present activated carbon nanotubes (P-CNTs) with abundant active edge sites and oxygen species for simultaneous achieving the activation of sidewalls and open ends. Also, the positive effects of oxygen species are decoupled by experimental data together with theoretical analysis. When capitalizing on the P-CNTs as the CE of DSSCs, the device delivers a high power conversion efficiency of 8.35% and an outstanding electrochemical stability, outperforming that of Pt reference (8.04%). The density functional theory calculation reveals that compared with the carboxylic groups, the hydroxyl groups and carbonyl groups on the surface of CNTs can greatly reduce the ionization energy of reaction, accelerate the electron transfer from external circuit to triiodide, thus being responsible for an enhanced electrocatalytic performance. This work demonstrates that a certain amount of oxygen atoms within carbon materials is also indispensable for the improvement in the reactivity of the triiodide.
关键词： Counter electrodes,Triiodide reduction,Defective carbon nanotubes,Ionization energy,Electrochemical stability,Oxygen species
更新于2025-09-23 15:23:52
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Rydberg-state ionization dynamics and tunnel ionization rates in strong electric fields
摘要： Tunnel ionization rates of triplet Rydberg states in helium with principal quantum numbers close to 37 have been measured in electric fields at the classical ionization threshold of ～197 V/cm. The measurements were performed in the time domain by combining high-resolution continuous-wave laser photoexcitation and pulsed electric field ionization. The observed tunnel ionization rates range from 105 to 107 s?1 and have, together with the measured atomic energy-level structure in the corresponding electric fields, been compared to the results of calculations of the eigenvalues of the Hamiltonian matrix describing the atoms in the presence of the fields to which complex absorbing potentials have been introduced. The comparison of the measured tunnel ionization rates with the results of these, and additional calculations for hydrogenlike Rydberg states performed using semiempirical methods, have allowed the accuracy of these methods of calculation to be tested. For the particular eigenstates studied the measured ionization rates are ～5 times larger than those obtained from semiempirical expressions.
关键词： Rydberg states,tunnel ionization,electric field ionization,complex absorbing potentials,helium
更新于2025-09-23 15:22:29
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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) - An Improved Random Path Length Algorithm for p-i-n and Staircase Avalanche Photodiodes
摘要： We present an improved Random Path Length algorithm to accurately and efficiently estimate the design space of heterostructure avalanche photodiodes (APDs) in terms of gain, noise and bandwidth without any need of full Monte Carlo transport simulations. The underlying nonlocal model for impact ionization goes beyond the Dead Space concept and it is suited to handle staircase structures composed by a superlattice of III-V compounds as well as thick and thin p-i-n APDs. The model parameters have been calibrated on GaAs and Al_xGa_{1-x}As p-i-n APDs in a previous work. In this work GaAs p-i-n APDs are compared to staircase structures in terms of noise and bandwidth.
关键词： Impact Ionization,Avalanche Multiplication,Random Path Length,Staircase APDs,Bandwidth,Excess Noise Factor,Simulation
更新于2025-09-23 15:22:29