Optical Energy Loss Function Research Articles

Molecular-scale kinetic Monte Carlo simulation of pattern formation in photoresist materials for EUV nanolithography

A kinetic Monte Carlo (KMC) simulation tool for modeling the pattern formation process in photoresist materials for extreme ultraviolet (photon energy 92 eV) nanolithography is presented. The availability of such a tool should support the progress toward novel materials and experimental procedures that lead to an improved pattern resolution. The molecular-scale simulations describe the process in a stochastic and mechanistic manner and include the excitation of high-energy electrons upon light absorption, the creation of a charged-particle cloud, electron-induced chemical degradation of the photoresist molecules, the resulting bond formation between neighboring degraded molecules, and a chemical development step after which a pattern of the remaining non-dissolved molecules is obtained. The method is applied to the application-relevant class of Sn-oxocore photoresist materials and uses their known electronic structure and optical electron energy loss function. The validity of the approach is tested by comparing measured and simulated total electron yield spectra and photoelectron spectra. A demonstration of the method is given by calculating the dose and pitch dependent average shape and stochastic variability (line edge roughness) of line patterns that are obtained for rectangular and sine-wave illumination, assuming various scenarios that determine how molecular-scale degradation will lead to bond creation. We show how from these simulations the ultimate pattern resolution can be deduced. The findings are analyzed systematically using results of KMC simulations that reveal the size of the cloud of degraded molecules around a point of absorption (blur length) and that further reveal the sensitivity to uniform illumination (contrast curves), and using percolation theory. We find that KMC modeling captures the consequences of the strong gradients in the density of degraded molecules and of the stochasticity of the patterning process that simplified models do not include, leading to a significantly improved view of the final pattern quality.

Structural, optical and electrical conduction characteristics of PMMA/PVAc/TBAI blended polymers

Structural, optical and electrical conduction characteristics of PMMA/PVAc/TBAI blended polymers

Chemical effect of alkaline-earth metals (Be, Mg, Ca) substitution of BFe2XH hydride perovskites for applications as hydrogen storage materials: A DFT perspective

Chemical effect of alkaline-earth metals (Be, Mg, Ca) substitution of BFe2XH hydride perovskites for applications as hydrogen storage materials: A DFT perspective

Impact of boron substitution on the thermoelectric, mechanical stability, electronic and optical properties of InP alloys

Impact of boron substitution on the thermoelectric, mechanical stability, electronic and optical properties of InP alloys

Electron backscattering coefficients for Cr, Co, and Pd solids: A Monte Carlo simulation study

We have calculated electron backscattering coefficients, η(Ep), at primary electron energies Ep of 0.1–100 keV for three elemental and intermediate atomic number solids, Cr, Co and Pd, with an up-to-date Monte Carlo simulation model. A relativistic dielectric functional approach is adopted for the calculation of the electron inelastic cross section, where several different datasets of optical energy loss function (ELF) are adopted. The calculated backscattering coefficient is found to be substantially affected by the ELF, where the influence can be seen to follow the f- and ps-sum rules and the resultant energy dependence of electron inelastic mean free path. To understand the uncertainties involved in a comparison with experimental data both the theoretical uncertainty due to the elastic cross-section model and the experimental systematic error for the contaminated surfaces are investigated. A total of 192 different scattering potentials are employed for the calculation of Mott's electron elastic cross section and this theoretical uncertainty is confirmed to be small. On the other hand, the simulation of contaminated Co and Pd surfaces with several carbonaceous atomic layers can well explain the experimental data. The present results indicate that accurate backscattering coefficient data should be either measured from fully cleaned surfaces or obtained from modern Monte Carlo theoretical calculations involving reliable optical constants data. With the recent progress in the accurate measurement of optical constants by reflection electron energy loss spectroscopy technique, constructing a reliable theoretical database of electron backscattering coefficients for clean surfaces of elemental solids is highly hopeful.

Uncertainty evaluation of Monte Carlo simulated line scan profiles of a critical dimension scanning electron microscope (CD-SEM)

In recent years, precision and accuracy for a more precise critical dimension (CD) control have been required in CD measurement technology. CD distortion between the measurement by a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important factor for a more accurate CD measurement. CD bias varies by a CD-SEM and a pattern condition. Therefore, it is urgently needed to identify, characterize, and quantify those parameters that may or may not affect the CD measurement by a CD-SEM. The sensitivity of the Monte Carlo simulated CD-SEM images with multiple physical modeling components has been studied previously. In this study, we demonstrate that the work function and elastic scattering potential models have a significant impact on secondary electron emission intensity, but their influence on the shape of the linescan profile is small, and other factors like the optical energy loss function and dielectric function models have even smaller effects. We have evaluated the uncertainty in the linescan profiles of Si line structures with different sidewall angles due to several different physical factors. It is found that when the CD is evaluated by a peak/valley method, the uncertainty of the CD is negligible. Therefore, it is concluded that the CD value and its related uncertainty are not critically related to the physical factors of the present Monte Carlo simulation model but rely dominantly on the line structure and electron beam parameters.

Determination of electron inelastic mean free path and stopping power of hafnium dioxide

We present inelastic mean free path (IMFP) and stopping power data of the hafnium dioxide applying the relativistic dielectric response theory. The energy loss function (ELF) derived from reflection electron energy loss spectroscopy spectrum with the reverse Monte Carlo method was used for the first time to obtain the IMFP and stopping power of HfO2. The probability of the energy loss is determined by the dielectric response function εq,ω as a function of the frequency ω and the wavenumber q of the electromagnetic disturbance. Two algorithms, namely the full Penn algorithm (FPA) and the super-extended Mermin algorithm (SMA), were employed to expand the optical energy loss function, Im-1/ε0,ω, into the q,ω-plane. The results indicate that the IMFP and the stopping power obtained by using both algorithms are consistent at high electron energies, but show differences at low electron energies (less than ∼ 70 eV). This discrepancy arises from the consideration of the finite plasmon lifetimes effect in the SMA model, while it is neglected in the FPA model. Additionally, we observed that the band gap has a significant influence on the IMFP and the stopping power at low electron energies. Typically, the inclusion of the band gap leads to an increase in the IMFP, because transition channels with energies larger than E-Eg-Ev are prohibited.

An extensive theoretical quantification of secondary electron emission from silicon

Though intensive experimental studies have been carried out on electron emission properties in past decades, the reliable data from accurate experimental measurements for clean and smooth surfaces are still quite limited. In this work, we have performed a comprehensive Monte Carlo simulation of electron emission yields, the secondary electron yield (SEY, δ), backscattered electron coefficient (BSC, η) and total electron yield (TEY, σ=δ+η), from silicon and the uncertainty quantification of the theoretical calculation results for the first time. The simulations were made on total 17280 scattering models. The considered uncertainty factors in the physical modelling that can influence the calculated yields include work function data, optical energy loss function data, dielectric function models for electron inelastic scattering and the scattering potentials for electron elastic scattering. The calculation results show that δ is significantly influenced by the work function while the dielectric function model has a slight effect. Elastic scattering potential (or elastic scattering cross section) and energy loss function affects to a certain extent both δ and η. Our simulated η data agree with most of the experimental measurements while the simulated mean δ data are well below most of the experimental data. At a 75% level of confidence, the experimental σ data measured by Goto et al. lie within the uncertainty range of our simulation results. This work has provided sufficient ground for the necessity of building a theoretical database of electron emission yield considering the fact that most of the previous experimental data are not reliable due to the presence of surface contamination during the measurements.

Charge Carrier Statistics-Based Analytical Model and Simulation of Optical Mechanisms in White Graphene for High-Quality FETs and Optoelectronic Applications

The aim of the present paper is to investigate the scaling behaviors of charge carriers and optical mechanisms in white graphene. The approach in this work is to provide analytical models for carrier velocity, carrier mobility, relaxation time and optical mechanisms of white graphene such as optical conductivity, absorption, transmittance, reflectivity, extinction coefficients and electron energy loss function. For doing so, one starts with identifying the analytical modeling of carrier concentration in the degenerate and nondegenerate regions. The computational models of carrier velocity, mobility and relaxation time with numerical solutions are analytically derived, in which the normalized Fermi energy, carrier concentration and temperature characteristics dependence are highlighted. Moreover, the optical mechanisms of white graphene are analytically modeled based on degenerate conductance. The proposed analytical models demonstrate a rational agreement with our simulation results and previous experiments in terms of trend and value. The remarkable properties of white graphene mentioned in this paper and obtained results bring new hopes for using of white graphene as a good substrate for nanomaterials such as graphene, germanene, stanene and silicene in electronics and optoelectronic applications.

Linear and Nonlinear Optical Properties of PVA:SA Blend Reinforced by TiO2 Nanoparticles Prepared by Flower Extract of Aloe Vera for Optoelectronic Applications

In this study, a polyvinyl alcohol–sodium alginate blend, PVA:SA 3:1 (w:w), was doped with different contents of TiO2 nanoparticles (NPs) prepared by aloe vera leaf extract to form the investigated nanocomposites. The nonlinear parameters of third-order susceptibility (χ(3)) and refractive index (n2) were detected by using UV-Vis spectroscopy and Z-scan techniques. Some different optical parameters were also determined, including the refractive index (n), optical dielectric parameters, volume and surface energy loss functions, and some others. The best solar skin protection factor (SSPF) was investigated by 5 wt.% of TiO2 NPs doped in PVA:SA 3:1, which was about 84.6% compared to the corresponding value of the host blend (41%). The studied nanocomposites were examined for their utility in the optical limiting of CUT-OFF laser filters utilizing a continuous He-Ne laser working at 632.2 nm. As a result, our finding demonstrated that TiO2 NPs doped in the host blend of PVA:SA positively influences a laser light blocking for the investigated laser source. Using the estimated gap energies values, different models were used to deduce theoretical values of the linear refractive index (n). The presence of Ti peaks in the EDX spectrum confirmed the doping of TiO2 NPs in the nanocomposites. SEM showed that the TiO2 NPs are homogeneously dispersed through the host blend with some agglomerates. XRD spectra showed that the values of the lattice strain εstr. detected at 2ϴ = 19.78° are 0.058, 0.055, and 0.060, corresponding to 1, 3, and 5 wt.% of TiO2 NPs doped in the PVA:SA blend.

Divulging the Potential of Sodium Carbide Thin Film for Semiconductor Applications

The work reported in this article is an attempt to introduce the least explored sodium carbide as a thin film and to explore its semiconducting behavior. The sodium carbide thin film deposited by the radio frequency sputtering technique is subjected to morphology, structure, and spectroscopic characterizations. The floral petal‐like morphology, understood from the field‐emission scanning electron microscopy and atomic force microscopy images, helps in enhancing interaction with the radiation that is revealed through the UV–visible absorption spectrum. X‐ray diffraction, photoelectron and Raman spectroscopic analyses confirm that the film is sodium carbide. The optical emission behavior of the sodium carbide thin film in the blue region is unveiled through the photoluminescence spectrum, power spectrum, color purity, and chromaticity diagram. Employing the refractive index and extinction coefficient values from the specular reflectance data, optical and electrical conductivities, nonlinear refractive index, linear and nonlinear optical susceptibility, dissipation factor, and surface and volume energy loss functions and their wavelength dependence due to interfacial polarization are investigated. The transfer matrix method is used to understand the spatial variation of the induced electric field and optical current density.

First-principles calculations to investigate mechanical, electronic, optical, and thermodynamic properties of Zr-based ternary compounds

First-principles calculations to investigate mechanical, electronic, optical, and thermodynamic properties of Zr-based ternary compounds

Extraction of Optical Constants and Dispersion Parameters of CdTe/CdSe Bi-Layer Thin Films

The current study focuses on the annealing-induced changes in the optical constants and dispersion parameters of the CdTe/CdSe bi-layer films deposited onto glass substrates by thermal evaporation technique. The slight shift in transmission threshold towards higher wavelength region with increasing annealing temperature revealed the systematic reduction in optical energy band gap (1.92 to 1.37 eV) of the films. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal dispersion in the transparent region. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion parameters and dielectric constants were evaluated. The increase in the refractive index with the annealing temperature modified the other linear parameters such as optical density, dissipation factor, volume, and surface energy loss function. The increase in the optical conductivity value is good for the CdSe film to be used as a semitransparent solar cells absorbing layer.We have made an attempt to discuss and correlate these results with the annealing temperature of possible mechanisms underlying the phenomena.

Chemical Bath Deposition Grown Zno Thin Films: Role of Manganese Doping

In this study, the effect of Mn doping concentration on the structural, microstructural, linear and nonlinear optical properties of ZnO was investigated. Pristine and Mn-doped ZnO films were prepared by chemical bath deposition on a glass substrate. The crystal structure and surface morphology of the films were determined by X-ray diffraction and force electron scanning microscopy (FESEM). X-Ray Diffraction (XRD) analysis revealed that the films had a polycrystalline structure and all films were ZnO with a hexagonal structure. In addition, a shift was detected in the XRD pattern of the films with the Mn doping process. According to the FESEM results, the surface of the films has irregularly shaped particles. Linear and nonlinear optical parameters were estimated using transmittance and absorbance measurements. And then, optical absorption coefficient, extinction coefficient, refractive index, optical dielectric constants, surface, and volume energy loss functions, optical band gap values, and optical and electrical conductivity were determined as linear optical properties. It was determined that these properties were affected by Mn-doped ratios. It was determined that nonlinear optical properties such as linear optical properties were also affected by the doping process.

First Principles Calculations of the Optical Response of LiNiO2

We discuss optical properties of layered Lithium Nickel oxide (LiNiO2), which is an attractive cathode material for realizing cobalt-free lithium-ion batteries, within the first-principles density functional theory (DFT) framework. Exchange correlation effects are treated using the generalized gradient approximation (GGA) and the strongly-constrained-and-appropriately-normed (SCAN) meta-GGA schemes. A Hubbard parameter (U) is used to model Coulomb correlation effects on Ni 3d electrons. The GGA+U is shown to correctly predict an indirect (system wide) band gap of 0.46 eV in LiNiO2, while the GGA yields a bandgap of only 0.08 eV. The calculated refractive index and its energy dependence is found to be in good agreement with the corresponding experimental results. Finally, our computed optical energy loss function yields insight into the results of recent RIXS experiments on LiNiO2.

Stibnite at modified Becke-Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb2S3), a chalcogenide binary material is intensively investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient one, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, a computational study of the structural, electronic and optical properties of the stibnite (Sb2S3) crystal structure is presented using the full potential (FP) linearized augmented plane wave (LAPW) method framed within the density functional theory (DFT). For the estimation of the exchange-correlation potential part, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA) Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew-Burke-Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA), the Trans-Blaha approach of the modified Becke-Johnson (TB-mBJ) potential is used to improve the fundamental band gap value. Moreover, these calculations are performed by involving spin-orbit coupling (SOC) contribution as well. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity absorption coefficient, refractive index, reflectivity, and electron energy loss function were investigated as well. The obtained results of the band gap energy and optical properties with TB-mBJ potential were found closer to the experimental data and endorse its potentiality for the photovoltaics applications.

Evaluation of electronic and optical behavior of the interface of Co2FeAl/AlN heusler alloy

Based on the density functional theory, the electronic, optical, and structural properties of the Co2FeAl/AlN Interface have been studied. It is shown that the Co2FeAl compound is a half-metal with 100% spin polarization at the Fermi level, and the growth of this compound on the AlN semiconductor changes its stability. The best interface connection from the point of view of stability occurs in the Co-Co-Al case, which has a semi-metallic and spin polarization of the interface, which candidate it for spintronic applications. The optical properties of this interface show that it can benefit medical and sensor devices because of its anisotropic optical properties at low energies. In the infrared, visible, and ultraviolet ranges, the optical energy loss functions are zero or very little, which referred to its candidate for optical applications in these energy ranges.

Evaluation of dielectric function models for calculation of electron inelastic mean free path

This work investigates the detailed difference between dielectric function models, the Mermin model and the full Penn algorithm (FPA) model, for the determination of an electron inelastic mean free path (IMFP) with optical energy loss function (ELF), as an extension of our previous study [Da et al., Surf. Interface Anal. 51, 627 (2019)] by using the simple Drude-type ELF. In the conventional normal Mermin (NM) model, the approximations of ELF by the Drude equation will introduce inevitable fitting error. In order to enhance the accuracy of the NM model, our previous proposed extended Mermin model [Da et al., Phys. Rev. Lett. 113, 063201 (2014)], which is renamed as a super-extended Mermin algorithm (SE-MA) now, is employed to eliminate the error by expanding the definition of Drude oscillators used in the NM. In the SE-MA, the Drude-like oscillators allow the existence of negative strengths to express the fine structures of phonon–electron scattering and the plasmon lifetime broadening effect. Because in our previous study, the simple Drude-type ELF cannot include these complex structures, in this work, the electron IMFPs are calculated for five realistic materials, Al, Si, Cu, Au, and MgO. The difference between IMFPs calculated by the SE-MA model and the FPA model is material dependent and is significant in the low energy region, which is analyzed by using the Fano plot. This is due to the more important role played by the plasmon lifetime broadening effect.

Effect of cycle numbers on the structural, linear and nonlinear optical properties in Fe2O3 thin films deposited by SILAR method

Fe 2 O 3 thin films were deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method onto glass substrates at different cycle numbers to investigate structural, linear and nonlinear optical properties. X-Ray Diffraction (XRD) analysis revealed that the Fe 2 O 3 thin films have a non-crystalline nature. The morphological properties of the films were investigated by Field Emission-Scanning Electron Microscopy (FE-SEM) and the results show that the films’ surfaces are porous. The linear and nonlinear optical parameters were evaluated and analyzed by using transmittance and absorbance measurements. For these measurements, UV–Vis spectroscopy at room temperature was used. The refractive index values were calculated in the range of 1.45–3.23 for visible region (400–700 nm). Obtained results reveal that direct optical band gap changed between 2.62 and 2.68 eV and indirect optical band gap changed between 1.67 and 1.77 eV. Additionally, optical electronegativity, optical dielectric constants, surface and volume energy loss functions, nonlinear refractive index, linear optical susceptibility, third-order nonlinear optical susceptibility, optical and electrical conductivity, and loss tangent values were calculated and discussed in detail. It was found that each parameter studied is dependent on the cycle numbers. Also, it can be stated that Fe 2 O 3 thin films are promising candidate for solar cells and optoelectronic device technology. Figure The change of a) linear optical susceptibility and b) third order nonlinear optical susceptibility values as function of wavelength for Fe 2 O 3 thin films. It can be seen from Fig. 14(a) that the linear optical susceptibility ( χ (1) ) values of Fe 2 O 3 thin films changed in the range of 0.088–0.753 in the visible region. It starts to decrease in the wavelength range of 400–600 nm and become stable at higher values of 600 nm. On the other hand, χ (1) values decrease with increasing the cycle numbers. Moreover the third order nonlinear optical susceptibility ( χ (3) ) values are in the range of 1.047 × 10 −11 –5.474 × 10 −8 esu in the visible region. This value decreases sharply in the 400–500 nm wavelength range and are almost constant at wavelengths higher than 500 nm. These values support usage of F 2 O 3 thin films for optoelectronic device and solar cell technologies. • Fe 2 O 3 thin films were fabricated successfully by Successive Ionic Layer Adsorption and Reaction (SILAR) method onto glass substrates. • Refractive index and other optical parameters were determined. • Direct and indirect optical band gap was calculated using the Tauc plot. • Linear optical susceptibility, third-order nonlinear optical susceptibility and nonlinear refractive index were calculated. • The physical and optical properties indicated strong dependence on cycle number.

Optical constants, dispersion parameters and energy loss functions of crystal violet as a potential absorber thin film for solar energy conversion and storage applications

Highly homogenous crystal violet (CV) thin films are grown by spin coating technique. X-ray diffraction (XRD) measurements have been carried out to identify the dominant orientation of the films. The XRD pattern of as-deposited film showed an amorphous structure which turns into nanocrystalline by thermal annealing at 150 °C for 1 h. The spectroscopic characterization of as-deposited and annealed CV films was estimated via spectrophotometric measurements of transmission and reflection in the spectral range 190–2000 nm. Optical constants of CV films were determined. Wemple-DiDomenico model was applied to the normal dispersion region of refractive index spectrum and from which, many dispersion parameters were calculated. The type of most probable transitions and values of optical energy gaps for CV films were estimated by Tauc plot. The dissipation energy and volume & surface loss functions were estimated. The influence of annealing temperature on the spectroscopic properties, dispersion parameters and energy loss functions were investigated which revealed an improvement in the optical properties and decreased values of energy loss functions for the annealed CV films. The obtained results of optical features for CV films reveals that CV films are an excellent potential absorbing material in solar energy conversion and storage devices. • Thin films of Crystal violet (CV) are grown by spin coating technique. • The XRD patterns of CV thin films have been investigated. • The optical constants of CV thin films have been calculated. • Dispersion parameters of CV films were calculated via single oscillator theory. • Energy loss functions of CV films were evaluated.