Model Dielectric Function Research Articles

Traversing of fast electrons in dense plasmas with dynamical screening

The traversing of fast electrons in dense D and T plasmas is discussed by different models with dynamical screening by means of dielectric functions. The traversing process is caused by a series of binary collision. It is found that the screening model with a classical dielectric function and Debye screening model only work in hot plasmas. Even for warm dense plasmas, the screening model with quantum dielectric function is reliable, which is well reproduced by the model with quantum static dielectric function. The related reasons are explored thoroughly. This work is helpful to study the transport of electrons in fully ionized dense plasmas.

Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa2O4

We report the elevated temperature (22 °C ≤ T ≤ 600 °C) dielectric function properties of melt grown single crystal ZnGa2O4 using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) × 10−5 K−1. A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M0-type critical point associated with the direct bandgap transition in ZnGa2O4 is shown to red-shift linearly as the temperature is increased with a subsequent slope of −0.72(4) meV K−1. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions.

Application of the Martin-Donoso-Zamudio multipole approximation for generalized Faddeeva/Voigt broadening of model dielectric functions

Faddeeva/Voigt broadening of dielectric functions (DFs) couples the physical properties of mutual Lorentzian and Gaussian broadening as a combined unit. This work investigates accurate computations for the general Faddeeva/Voigt broadening of complex analytic DFs and their derivatives. The paper builds on the multipole approximation for broadening profiles and exploits the reduction of the approximation into a finite sum of Lorentzian profiles. Using a two-point Padé approximant for the Faddeeva function, we computed this study's twenty-pole Martin-Donoso-Zamudio (MDZ20) approximation. First, we evaluated the accuracies of the MDZ20 approximation relative to high-precision evaluation of the Faddeeva function and its first three derivatives. Second, we applied the MDZ20 approximation to derive the general approximation formula for the Faddeeva/Voigt broadening of Kramer-Kronig-consistent complex analytic DFs. Third, we assessed the accuracy of Voigt broadening in two theoretical applications: the universal-dispersion model through piecewise polynomial elements and the three-dimensional (3D) M0 critical point and derivatives by using the MDZ20 approximation. Finally, we developed formulas for the Faddeeva/Voigt broadening of Tanguy's 3D excitons and the Tauc-Lorentz models. The Faddeeva/Voigt-broadened Tanguy model is investigated within Gilliot's dielectric model of sol-gel ZnO. The Faddeeva/Voigt-broadened Tauc-Lorentz model is applied to amorphous silicon (a-Si). Specifically, we evaluated the impact of adding a Gaussian component to each Lorentzian width on the agreement of the Voigt-broadened DF to experimental data.

Temperature-dependent optical properties of ε-Ga2O3 thin films

We determined the complex dielectric functions of ε-Ga2O3 using optical transmittance and reflectance spectroscopies at temperatures from 10 K to room temperature. The measured dielectric-function spectra reveal distinct structures at bandgap energy. We fitted a model dielectric function based on the electronic energy-band structure to these experimental data. We analyzed the temperature dependence of the bandgap with a model based on phonon dispersion effects. One could explain it in terms of phonon-related parameters such as the optical phonon temperature. We compare phonon-related properties of ε-Ga2O3 with those of a large variety of element and binary semiconductors.

Optical constants of organic insulators in the UV range extracted from reflection electron energy loss spectra

Reflection electron energy loss spectroscopy (REELS) spectra were measured for seven insulating organic compounds (DNA, Irganox 1010, Kapton, polyethylene [PE], poly(methyl methacrylate) [PMMA], polystyrene [PS] and polytetrafluoroethylene [PTFE]). Optical constants and energy band gaps were extracted from the measured REELS spectra after elimination of multiple electron scattering via a deconvolution and fitting the normalised single scattering energy loss spectra to Drude and Drude–Lindhard model dielectric functions, constrained by the Kramers–Kronig sum and f‐sum rules. Satisfactory agreement is found for those optical constants for which literature data exists. For PTFE, the observed features in the optical data correspond to its electronic structure.

Iridium (IV) Oxide (IrO<SUB>2</SUB>) Smart Nano Particles, Nano Capsules and Nanoclusters Influence, Impression and Efficacy in Cancer Prevention, Prognosis, Diagnosis, Imaging, Screening, Treatment and Management under Synchrotron and Synchrocyclotron Radiations

In the current research, advanced studies on the effect of transition metal doped Iridium (IV) Oxide (IrO2) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations is investigated. The calculation of thickness and optical constants of Iridium (IV) Oxide (IrO2) advanced studies on the effect of transition metal doped Iridium (IV) Oxide (IrO2) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations produced using sol-gel method over glassy medium through a single reflection spectrum is presented. To obtain an appropriate fit for reflection spectrum, the classic Drude-Lorentz model for parametric di-electric function is used. The best fitting parameters are determined to simulate the reflection spectrum using Lovenberg-Marquardt optimization method. The simulated reflectivity from the derived optical constants and thickness are in good agreement with experimental results.

Ruthenium (IV) Oxide (RuO 2 ) and Ruthenium (VIII) Oxide (RuO 4 ) Smart Nano Particles, Nano Capsules and Nanoclusters Influence, Impression and Efficacy in Cancer Prevention, Prognosis, Diagnosis, Imaging, Screening, Treatment and Management under Synchrotron and Synchrocyclotron Radiations

In the current research, annealing effects on the interband transition and optical constants of Ruthenium (IV) Oxide (RuO₂) and Ruthenium (VIII) Oxide (RuO4) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations is investigated. The calculation of thickness and optical constants of Ruthenium (IV) Oxide (RuO₂) and Ruthenium (VIII) Oxide (RuO4) annealing effects on the interband transition and optical constants of Ruthenium (IV) Oxide (RuO₂) and Ruthenium (VIII) Oxide (RuO4) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations produced using sol-gel method over glassy medium through a single reflection spectrum is presented. To obtain an appropriate fit for reflection spectrum, the classic Drude-Lorentz model for parametric di-electric function is used. The best fitting parameters are determined to simulate the reflection spectrum using Lovenberg-Marquardt optimization method. The simulated reflectivity from the derived optical constants and thickness are in good agreement with experimental results.

The Effect of Solution Molarity on the Structural, Morphological, Optical and Electrical Properties of Nanostructured Cadmium Oxide (CdO) Nano Thin Films as Anti-Cancer Nano Drug in Cancer Cells, Tissues and Tumors under Synchrotron and Synchrocyclotron Radiations

In the current research, the effect of solution molarity on the structural, morphological, optical and electrical properties of nanostructured Cadmium Oxide (CdO) nano thin films as anti-cancer nano drug in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations is investigated. The calculation of thickness and optical constants of Cadmium Oxide (CdO) the effect of solution molarity on the structural, morphological, optical and electrical properties of nanostructured Cadmium Oxide (CdO) nano thin films as anti-cancer nano drug in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations produced using sol-gel method over glassy medium through a single reflection spectrum is presented. To obtain an appropriate fit for reflection spectrum, the classic Drude-Lorentz model for parametric di-electric function is used. The best fitting parameters are determined to simulate the reflection spectrum using Lovenberg-Marquardt optimization method. The simulated reflectivity from the derived optical constants and thickness are in good agreement with experimental results. Keywords: Tructural; Morphological; Optical and Electrical Properties; Nanostructured Cadmium Oxide (CdO); Nano Thin Films; Anti-Cancer Nano Drug; Cancer Cells; Tissues and Tumors; Synchrotron and Synchrocyclotron Radiations

Removal Role, Application and Effect of Nanocluster Rhenium (IV) Oxide (ReO2), Rhenium Trioxide (ReO3) and Rhenium (VII) Oxide (Re2O7) Thin Films Delivery in DNA/RNA of Cancer Cells under Synchrotron and Synchrocyclotron Radiations

In the current research, removal role, application and effect of nanocluster Rhenium (IV) Oxide (ReO2), Rhenium Trioxide (ReO3) and Rhenium (VII) Oxide (Re2O7) thin films delivery in DNA/RNA of cancer cells under synchrotron and synchrocyclotron radiations is investigated. The calculation of thickness and optical constants of Rhenium (IV) Oxide (ReO2), Rhenium Trioxide (ReO3) and Rhenium (VII) Oxide (Re2O7) removal role, application and effect of nanocluster Rhenium (IV) Oxide (ReO2), Rhenium Trioxide (ReO3) and Rhenium (VII) Oxide (Re2O7) thin films delivery in DNA/RNA of cancer cells under synchrotron and synchrocyclotron radiations produced using sol-gel method over glassy medium through a single reflection spectrum is presented. To obtain an appropriate fit for reflection spectrum, the classic Dude-Lorentz model for parametric di-electric function is used. The best fitting parameters are determined to simulate the reflection spectrum using Levenberg-Marquardt optimization method. The simulated reflectivity from the derived optical constants and thickness are in good agreement with experimental results. Keywords: Removal; Nanocluster Rhenium (IV) Oxide (ReO2); Rhenium Trioxide (ReO3) and Rhenium (VII) Oxide (Re2O7); Thin Films, Delivery; DNA/RNA; Cancer Cells; Synchrotron and Synchrocyclotron Radiations

Annealing Effects on the Interband Transition and Optical Constants of Ruthenium (IV) Oxide (RuO2) and Ruthenium (VIII) Oxide (RuO4) Nano Thin Films in Cancer Cells, Tissues and Tumors under Synchrotron and Synchrocyclotron Radiations

In the current research, annealing effects on the interband transition and optical constants of Ruthenium (IV) Oxide (RuO?) and Ruthenium (VIII) Oxide (RuO4) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations is investigated. The calculation of thickness and optical constants of Ruthenium (IV) Oxide (RuO2) and Ruthenium (VIII) Oxide (RuO4) annealing effects on the interband transition and optical constants of Ruthenium (IV) Oxide (RuO2) and Ruthenium (VIII) Oxide (RuO4) nano thin films in cancer cells, tissues and tumors under synchrotron and synchrocyclotron radiations produced using sol-gel method over glassy medium through a single reflection spectrum is presented. To obtain an appropriate fit for reflection spectrum, the classic Drude-Lorentz model for parametric di-electric function is used. The best fitting parameters are determined to simulate the reflection spectrum using Lovenberg-Marquardt optimization method. The simulated reflectivity from the derived optical constants and thickness are in good agreement with experimental results. Keywords: Annealing, Interband Transition; Optical Constants; Ruthenium (IV) Oxide (RuO2) and Ruthenium (VIII) Oxide (RuO4); Nano Thin Films; Cancer Cells; Tissues and Tumors; Synchrotron and Synchrocyclotron Radiations

Optical properties of LiNbO2 thin films

The complex dielectric functions of LiNbO2 were determined using optical transmittance and reflectance spectroscopies at room temperature. The measured dielectric function spectra reveal distinct structures at several bandgap energies. The bandgaps (exciton resonances) in the spectrum were observed at ca. 2.3, 3.2, 3.9, and 5.1 eV, respectively. These experimental data have been fit using a model dielectric function based on the electronic energy-band structure near critical points plus excitonic effects. The features of measured dielectric functions are, to some extent, reproduced quantitatively by an ab-initio calculation including the interaction effects between electrons and holes.

Use of interface phonon-polaritons for the alloy determination in ZnO/(Zn,Mg)O multiple quantum wells

A method based on infrared reflectance spectroscopy is presented by which the Mg content in ZnO/(Zn,Mg)O multiple quantum wells with very thin barriers can be determined. The method relies on the observation of interface phonon-polaritons which appear as sharp dips in the p-polarized reflectance spectra at oblique incidence near the longitudinal optical (LO)-phonon frequencies of both QW and barrier materials. By fitting the reflectance spectra to a dielectric function model, the LO phonon frequency of the (Zn,Mg)O barrier layers can be determined. The LO phonon frequency depends on the Mg content. Comparing to Mg content calibration via cathodoluminescence, a linear relationship between the reflectance dip frequency and the Mg content is obtained. The presented method serves as a rapid means to determine the Mg content on final structures with very thin (Zn,Mg)O layers -such as device structures- where alternative, destructive methods cannot be used.

Fully automated spectroscopic ellipsometry analyses: Application to MoOx thin films

In spectroscopic ellipsometry, the optical properties of materials are obtained indirectly by generally assuming dielectric function and optical models. This ellipsometry analysis, which typically requires numerous model parameters, has essentially been performed by a trial-and-error approach, making this method as a rather time-consuming characterization technique. Here, we propose a fully automated spectroscopic ellipsometry analysis method, which can be applied to obtain dielectric functions of light absorbing materials in a full measured energy range without any prior knowledge of model parameters. The developed method consists of a multiple-step grid search and the following non-linear regression analysis. Specifically, in our approach, the analyzed spectral region is gradually expanded toward a higher energy, while incorporating an additional optical transition peak whenever the root mean square error of the fitting analysis exceeds a critical value. In particular, we have established a unique algorithm that could be employed for the ellipsometry analyses of different types of optical materials. The proposed scheme has been applied successfully for the analyses of MoOx transparent oxides and the complex dielectric function of a MoOx layer that exhibits dual optical transitions due to band-edge and deep-level absorptions has been determined. The developed method can drastically reduce a time necessary for an ellipsometry analysis, eliminating a serious drawback of a traditional spectroscopic ellipsometry analysis method.

Ellipsometric study of the optical properties of TlInSeS layered crystal

TlInSeS optical properties at photon energy ranges from 0.96 to 5.06 eV have been determined by means of variable-angle spectroscopic ellipsometry (VASE). This energy range contains the fundamental band gap. The measured pseudo-dielectric ε(E) spectrum depicts different peaks. The spectrum is analyzed with reference of two inter-band transitions models that postulated for crystal semiconductors, explicitly, critical point parabolic band (CPPB) and standard critical-point (SCP) models. It is noted that both dielectric function models illustrates the plausible agreement with the experiment ε(E) spectra. The optical properties of the present sample as extension coefficient refractive index absorption coefficient and the normal-reflectance, are investigated. The elemental composition of TlInSeS system has been confirmed by means of Energy Dispersive X-ray fluorescence spectrometer (EDXRF).

Spectroscopic Ellipsometry Characterization of As-Deposited and Annealed Non-Stoichiometric Indium Zinc Tin Oxide Thin Film.

A spectroscopic ellipsometry study on as-deposited and annealed non-stoichiometric indium zinc tin oxide thin films of four different compositions prepared by RF magnetron sputtering was conducted. Multi-sample analysis with two sets of samples sputtered onto glass slides and silicon wafers, together with the analysis of the samples onto each substrate separately, was utilized for as-deposited samples. Annealed samples onto the glass slides were also analyzed. Spectroscopic ellipsometry in a wide spectral range (0.2–6 eV) was used to determine optical constants (refractive index n and extinction coefficient k) of these films. Parameterized semiconductor oscillator function, together with Drude oscillator, was used as a model dielectric function. Geometrical parameters (layer thickness and surface roughness) and physical parameters (direct optical bandgap, free carrier concentration, mobility, and specific electrical resistivity) were determined from spectroscopic ellipsometry data modeling. Specific electrical resistivity determined from the Drude oscillator corresponds well with the results from electrical measurements. Change in the optical bandgap, visible especially for annealed samples, corresponds with the change of free carrier concentration (Moss–Burstein effect). Scanning electron microscope did not reveal any noticeable annealing-induced change in surface morphology.

Modeling the temperature dependence of the optical properties of anisotropic SnS0.52Se0.48

We report the parameter values of the model dielectric function ( $$\varepsilon = \varepsilon_{1} + i\varepsilon_{2}$$ ) of SnS0.52Se0.48 in the spectral range from 0.74 to 6.42 eV and the temperature range from 27 to 350 K. An analytic representation, obtained using the Tauc–Lorentz (TL) dispersion model, allows interpolation of the parameters with respect to both energy and temperature. We used reported experimental spectra as the basis of our approach and verified that the TL model can parameterize the model dielectric function so as to reproduce the experimental data well and yield values of the dielectric function and the refractive index at arbitrary temperatures that are useful for device applications.

High-temperature solar-selective coatings based on Cr(Al)N. Part 1: Microstructure and optical properties of CrNy and Cr1-xAlxNy films prepared by DC/HiPIMS

In order to explore the potentialities of Cr1-x(Al)xNy materials in multilayer-based solar selective coatings (SSC) for high temperature applications (T > 500 °C), the optical behavior of Cr1-x(Al)xNy films is studied in this work. Two sets of layers (CrNy and Cr1-xAlxNy) were prepared by direct current (DC) and high-power impulse magnetron sputtering (HiPIMS) technology. The deposition parameters: N2 flux, HiPIMS frequency and aluminum sputtering power, were modified to get a wide variety of stoichiometries. The composition, morphology, phases and electronic structure of the films were characterized in depth. The optical behavior was determined by UV–Vis–NIR and FTIR spectroscopies, and the optical constants were obtained from the measured transmittance and reflectance spectra based on appropriate dielectric function models. Our results indicate that small changes in the layer composition influence the optical constants. In particular, a metallic-like behavior was obtained for CrNy layers with N vacancies (CrN0.95 and CrN0.67 films) while a semiconductor-like behavior was observed for CrN1.08. Thus, the CrNy films can be used as effective absorber layer in multilayer-based SSC, and namely, the CrN0.67 film as an IR reflector/absorber layer too. Likewise, the optical properties of Cr1-xAlxNy layers can also be tuned from metallic to semiconductor-like behavior depending on the chemical composition. Indeed, the absorption coefficients of Cr1-xAlxNy films with optimized Al content and N-vacancies are comparable to those reported for state-of-the-art materials such as TiAlN or TiAlCrN. In addition, a Cr0.96Al0.04N0.89 film was found to be a suitable IR reflector/absorber layer.

Greatly enhanced solar absorption via high entropy ceramic AlCrTaTiZrN based solar selective absorber coatings

High entropy alloys (HEAs), which is at the expense of high cost compared to traditional alloy, should not be confined to the mechanical properties, but should be employed to devise a novel combination with unique functional and mechanical performances. In this work, high entropy alloy nitride (HEAN) is utilized as a novel double absorption layer to improve solar absorption in the high temperature solar selective absorbing coatings (SSACs). Our primary motivation is to lower thermal emittance (ε) and enhance solar absorptance (α). In order to realize this goal, coating design (CODE) software is employed to design and optimize the proposed HEAN based SSACs using appropriate dielectric function model. The ultimate as-deposited coating shows good optical properties with a high α value of 0.965 and a low ε value of 0.086 (at 82 °C). The estimate of thermal stability tests indicates that HEAN based SSACs has the ability to resist instability in high working temperature, which keeps good optical properties (α = 0.925, ε = 0.070) after annealing at 600 °C for 10 h.

Study on the mechanism of a femtosecond laser-induced breakdown of the deposited substrate mediated by aluminum nanoparticles in a vacuum

The mechanism of a femtosecond laser-induced breakdown of deposited substrates mediated by aluminum nanoparticles in a vacuum environment was studied. This model of optical breakdown mediated by aluminum nanoparticles includes the electromagnetic field model for the description of near-field enhancement of aluminum nanoparticles, the two-temperature model for the description of electron and lattice temperature of aluminum nanoparticles, and the plasma model for the description of the evolution of electron density in the deposited substrate. These three physical field models were fully coupled in this model. We defined a new modified dielectric function model to describe the dielectric function of aluminum nanoparticles, due to the strength of near-field enhancement depends on the size and morphology of nanoparticles. The near-field enhancement of different types of aluminum nanoparticles, the femtosecond laser breakdown threshold of deposited substrates, and the evolution of the lattice temperature of aluminum nanoparticles were investigated. The results showed that assembled aluminum nanoparticles can significantly reduce the femtosecond laser breakdown threshold of deposited substrates in a vacuum, and the lattice temperature of aluminum nanoparticle was lower than the melting point, under the irradiation of a single-pulse femtosecond laser with a wavelength of 800 nm and pulse width of 25 fs.

Analysis of the optical constants and bandgap energy in Al1-x In x N alloys grown on a c-plane freestanding GaN substrate by using spectroscopic ellipsometry

The optical constants and bandgap energy (E g) of semiconductors, characterized by spectroscopic ellipsometry (SE), are highly affected by the applied model dielectric function (MDF). In this study, we investigated the optical constants and E g in low indium content (x) Al1-x In x N alloys grown on a c-plane freestanding GaN substrate by using SE, and their applied MDF dependence was investigated. The tanΨ and cosΔ spectra, in a photon energy range of 1.5–5.0 eV, of high-quality crystalline Al1-x In x N alloys were well fitted by Adachi’s critical-point (ACP) model. The ACP model exhibited better spectral fitting results than did the Tauc–Lorentz model, which has often been adopted for Al1-x In x N alloys. The accuracy of the E g values obtained by the ACP model was confirmed by optical reflectance measurements. It is suggested that the ACP model is a suitable MDF for recent high-quality crystalline Al1-x In x N alloys as well as other III-nitride semiconductors.