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The description of quantum dielectric function for insulators over Bethe surface
摘要： A new expression for the dielectric function is suggested here, which is the Mermin–Belkacem-Sigmund (MBS) model derived from the Belkacem–Sigmund (BS) model based on the conservation of a local particle number in the Mermin model. The energy loss function expressions are reviewed analytically for both models, and these dielectric functions were used to calculate the Bethe sum rule, the energy loss function (ELF), as well as the differential inelastic inverse mean free path (DIIMP) for H2O. The indication from the results is that, compared to the BS dielectric function, the MBS dielectric function is more compatible in its consistency with the exact Bethe sum rule. The ELF for the MBS type is compatible relatively in high and low momentum transfers, while the ELF for the BS type is suitable for high-k. The two models of ELF were also applied to evaluate DIIMP for electron kinetic energy 1 keV, and these were compared with the results predicted in several ways via the SESINIPAC program, using the Mermin dielectric function and the extended Drude and Monte–Carlo method. These predicted results are in reasonable agreement with those estimated from other methods at the range of energy transfer (0–50) eV.
关键词： Bethe surface,differential inelastic inverse mean free path,local particle number,Energy loss function,dielectric function
更新于2025-09-23 15:23:52
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The Monte Carlo Simulation of Secondary Electrons Excitation in the Resist PMMA
摘要： The Monte Carlo method was used to simulate the process of secondary electrons excitation in resist PMMA with Mott cross section and dielectric function model. By analyzing the characteristics of secondary electrons excitation in the resist PMMA, and the simulation of secondary electrons energy range, we hold the opinion that the secondary electrons can not be ignored in the electron beam lithography.
关键词： Monte Carlo simulation,electron beam lithography (EBL),dielectric function,secondary electrons
更新于2025-09-23 15:23:52
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Hybrid functional calculations of electro-optical properties of novel Ga1a??xInxTe ternary chalcogenides
摘要： Doping GaTe semiconductor with indium can be beneficial in the realization of high-quality radiation detectors. In this study, first-principle calculations based on the density functional theory have been used to investigate the structural and electro-optical properties of Ga1?xInxTe alloys. For the electronic structure calculations, the exchange–correlation functionals are treated with an accurate PBE0 hybrid functional giving improved agreement with experimental band energies. The influence of the In concentration on the energy band gaps is analyzed. Furthermore, the direction for the highest mobility of Ga1?xInxTe is estimated by calculating the effective mass of carriers respecting to the crystallographic directions from calculated electronic band structures. Optical spectra of Ga1?xInxTe are evaluated for all compositions (x = 0, 0.25, 0.5 and 0.75) and for different polarization directions in the range of 0–14 eV. The calculated optical spectra of Ga1–xInxTe are found to have a remarkable redshift as the alloying composition increases. The calculated static dielectric constant for the entire concentration shows that the considered alloys are a high-dielectric constant materials. Our study shows that Ga1?xInxTe alloys exhibit metallic properties in some energy ranges. Our results suggest that the new Ga1?xInxTe alloys are a promising material for radiation detectors, microelectronics and optoelectronic devices.
关键词： First-principles calculations,Band structure,Effective mass,Ga1–xinxte,Dielectric function,PBE0 hybrid functional
更新于2025-09-23 15:21:01
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Opto-mechanics driven fast martensitic transition in two-dimensional materials
摘要： Diffusional phase-change materials, such as Ge-Sb-Te alloys, are used in rewritable non-volatile memory devices. But the continuous pursuit of readout/write speed and reduced energy consumption in miniaturized devices calls for optically driven, diffusionless phase change scheme in ultra-thin materials. Inspired by optical tweezers, in this work, we illustrate theoretically and computationally that a linearly polarized laser pulse with selected frequency can drive an ultrafast diffusionless martensitic phase transition of two-dimensional ferroelastic materials such as SnO and SnSe monolayers, where the unit-cell strain is tweezed as a generalized coordinate that affects the anisotropic dielectric function and electromagnetic energy density. At laser power of 2.0×1010 and 7.7×109 W/cm2, the transition potential energy barrier vanishes between two 90°-orientation variants of ferroelastic SnO and SnSe monolayer, respectively, so displacive domain switching can occur within picoseconds. The estimated adiabatic thermal limit of energy input in such optomechanical martensitic transition (OMT) is at least two orders of magnitude lower than that in Ge-Sb-Te alloy.
关键词： martensitic phase transition,ferroelasticity/ferroelectricity,two-dimensional materials,dielectric function,density functional theory,opto-mechanics
更新于2025-09-23 15:21:01
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Analyzing role of relaxation time on second harmonic generation and optical dielectric function of impurity doped quantum dots under the aegis of noise
摘要： Present study monitors the influence of relaxation time (τ) on second harmonic generation (SHG) and total optical dielectric function (TODF) of impurity containing quantum dot (QD) under the stewardship of Gaussian white noise. Two distinct roadways viz. ‘additive’ and ‘multiplicative’ have been exploited for the entrance of noise to the system. Both in absence and presence of noise the SHG and TODF peak positions do not exhibit any shift with increase in τ. The SHG peak values display monotonic behavior with the variation of τ. However, the TODF peak values delicately depend on variation of τ being guided by the presence of noise and also on its mode of introduction. Presence of additive (multiplicative) noise causes enhancement (suppression) of SHG and TODF peak values as τ varies over a range. The findings appear to be crucial in the fabrication of QD-based opto-electronic devices where role of noise deserves to be properly addressed.
关键词： Quantum dot,Gaussian white noise,Impurity,Total optical dielectric function,Relaxation time,Second harmonic generation
更新于2025-09-23 15:21:01
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Impact of dielectric environment on the linear and nonlinear optical properties for CdS/ZnS cylindrical core/shell quantum dots
摘要： By the mean of the effective mass approximation (E.M.A) and compact density matrix method, the energy eigenvalues, linear and nonlinear dielectric function have been theoretically investigated for CdS/ZnS cylindrical core/shell quantum dot embedded in PVA, PMMA and SiO2 matrices. Simulation results showed that the presence of the dielectric mismatch in the QD-matrix system can lead to a significant enhancement of the nonlinear dielectric function. According to our calculations, peaks of the real and imaginary part of the dielectric function can experience a redshift or a blue shift with the appropriate dielectric environment.
关键词： complex dielectric function,Effective mass approximation,cylindrical core/shell quantum dot,density matrix approach
更新于2025-09-23 15:19:57
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Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites
摘要： Among the exceptional properties of lead halide perovskites (LHPs) is the ultraslow cooling of hot carriers. Carrier densities below the Mott density for large polarons (≤ ≈1018 cm?3) are focused on here. As in other semiconductors, a nascent hot electron distribution initially cools down via emission of longitudinal optical (LO) phonons on the 10?14–10?13 s timescale. What distinguishes LHPs from conventional semiconductors is the exceptionally efficient screening in the former. The dielectric screening in LHPs on the 10?13 s timescale results in an order-of-magnitude reduction in the Coulomb potential upon the formation of a large polaron, likely with ferroelectric-like local ordering. Further LO-phonon emission is inhibited, and this leads to partial retention of hot electron energy on the 10?12 s timescale, more so in hybrid LHPs than in their all-inorganic counterparts. Further cooling of hot polarons occurs on the 10?10 s timescale, and this can be attributed to the slow diffusion of heat out of the large polaron volume due to the low thermal conductivity of LHPs. Like other carrier properties, slow hot carrier cooling in LHPs can be intimately related to efficient screening in a soft, anharmonic, and dynamically disordered lattice.
关键词： dielectric function,lead halide perovskites,screening,hot electrons,large polarons
更新于2025-09-19 17:15:36
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Laser beam self-focusing in collisional plasma with periodical density ripple
摘要： In the paper, we applied the paraxial region theory and Wentzel–-Kramers–-Brillouin approximation to study laser beam self-focusing in the interaction of laser and collisional plasma with periodical density ripple. The results have shown that, under the influence of collision nonlinear effect, laser presents stable self-focusing, self-defocusing, and oscillational self-focusing in the plasma. Besides, the parameters of plasma with periodical density ripple have a greater impact on the effect of self-defocusing and oscillational self-focusing than stable self-focusing. In certain conditions, beam self-defocusing and oscillational self-focusing would decline and even disappear, and stable self-focusing would further be strengthened. Hence, selecting a suitable periodic plasma system is advantageous for separating self-defocusing and oscillational self-focusing, and for the formation of a more stable collisional self-focusing.
关键词： self-focusing,dielectric function,Collisional plasma,periodical density ripple,electron temperature
更新于2025-09-19 17:13:59
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Dielectric environment effect on linear and nonlinear optical properties for CdS/ZnS core/shell quantum dots
摘要： The eigenvalues, transition energy, the linear and nonlinear dielectric functions have been numerically investigated for CdS/ZnS spherical core/shell quantum dots embedded in various dielectric matrices. The evaluation was carried out for three commonly used matrices, such as PVA, PMMA and SiO2. Calculations were done under the effective mass approximation and compact density matrix approach. Results revealed that the nonlinear optical property is strongly affected by the nature of the matrix material. By increasing core/shell radii ratio the energy states as well as the transition energy are decreasing. It is also indicated that the presence of the dielectric mismatch in the QD-matrix system can cause significant enhancement on the linear and third order nonlinear dielectric function.
关键词： Complex dielectric function,Core/shell,Density matrix approach,Effective mass approximation,Nonlinear optic
更新于2025-09-12 10:27:22
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Size-dependent dielectric function for electron-energy-loss spectra of plasmonic nanoparticles
摘要： A size-dependent complex dielectric function is proposed to describe the impact that size effects have on the dielectric response for electron energy loss spectroscopy (EELS) of plasmonic nanoparticles. Our implementation is based on experimental bulk complex refractive index and the modification of the Lorentz-Drude model. Our theoretical framework is verified and analysed by performing numerical simulation comparisons of EELS for Au spherical nanoparticles of different sizes. The results show that finite-size effects cannot be neglected for a broader size range of up to at least 200 nm for Au spherical nanoparticles. Moreover, the EELS regions in which contributions of surface or bulk energy loss are dominant are confirmed by the optical extinction spectra of Au spherical nanoparticles of different sizes, which takes into account the size-dependent dielectric function. The results provided here provide a suitable and versatile framework for the design of plasmonic elements on the nanometre scale.
关键词： metallic nanoparticles,Plasmonics,size-dependent dielectric function,surface plasmon,electron energy loss spectroscopy (EELS)
更新于2025-09-12 10:27:22