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In this research, we investigated the optical properties of CdSe thin films on glass substrates using spectroscopic ellipsometry. The samples were analysed using an M-2000 rotation compensator spectroscopic ellipsometer at room temperature, covering a photon energy range of 1.5-7.0 eV. We used an appropriate dispersion model to obtain the spectral dispersion of the optical constants. We calculated the thickness, dielectric permittivity (real and imaginary parts), refraction, and extinction coefficients of the thin layers. The results showed high transparency that varied with the size of the CdSe thin films. Additionally, we determined the bandgap width for samples with thicknesses of 350 nm and 400 nm, which were produced using the chemical deposition method. [ABSTRACT FROM AUTHOR]

Tungsten oxide (WO3) electrochromic devices are obtaining increasing interest due to their color change and thermal regulation. However, most previous work focuses on the absorption or transmission spectra of materials, rather than the optical parameters evolution in full spectrum in the electrochromic processes. Herein, we developed a systematic protocol of ex situ methods to clarify the evolutions of subtle structure changes, Raman vibration modes, and optical parameters of WO3 thin films in electrochromic processes as stimulated by dosage-dependent Li+ insertion. We obtained the below information by ex situ spectroscopic ellipsometry. (1) Layer-by-layer Li+ embedding mechanism demonstrated by individual film thickness analysis. (2) The details of its optical leap in the Brillouin zone in the full spectral. (3) The optical constants varied with the Li+ insertion in the ultraviolet, visible, and near-infrared bands, demonstrating the potential for applications in chip fabrication, deep-sea exploration, and optical measurements. (4) Simulated angular modulation laws of WO3 films for full spectra in different Li+ insertion states. This ex situ method to study the optical properties of electrochromic devices are important for monitoring phase transition kinetics, the analysis of optical leaps, and the study of ion diffusion mechanisms and the stoichiometry-dependent changes in optical constants over the full spectral. This work shows that electrochromic films in Li+ surface permeation can be applied in the field of zoom lenses, optical phase modulators, and other precision optical components. Our work provides a new solution for the development of zoom lenses and a new application scenario for the application of electrochromic devices. [ABSTRACT FROM AUTHOR]

The optical constants of single-crystal AlxGa1−xP and AlxGa1−xAs have been widely studied at various Al compositions but have not yet been thoroughly investigated as polycrystalline materials. Using variable-angle spectroscopic ellipsometry, we estimate and analyze the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As that were non-epitaxially deposited at deposition temperatures of either 250 or 420 °C, and with various dopant species, dopant concentrations, and V/III flux ratios. For wavelengths of 350–400 nm, decreasing the V/III ratio increases the refractive index of Be-doped polycrystalline Al0.25Ga0.75P. For wavelengths >500 nm, as the targeted Be dopant concentration increases for polycrystalline Al0.25Ga0.75P, the amount the extinction coefficient increases and the indirect bandgap decreases depends on the V/III ratio. Furthermore, Si-doped polycrystalline Al0.25Ga0.75P has significantly smaller extinction coefficient values than when it is Be-doped, for the same V/III ratio and targeted doping concentration, at wavelengths >500 nm. Based on our findings, we hypothesize that the dopant species, dopant concentration, and the V/III ratio dictate various types of defect concentrations, which then affect the optical constants and indirect bandgap of polycrystalline Al0.25Ga0.75P. Additionally, for wavelengths >500 nm, we find that polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As have the lowest extinction coefficient values when deposited at 420 °C, as opposed to 250 °C. Thus, we hypothesize that the deposition temperature is the most significant factor in dictating the optical constants of these polycrystalline III-Vs. Ultimately, this work demonstrates alternative methods to tune the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As, as opposed to tuning the Al composition. [ABSTRACT FROM AUTHOR]

A preliminary investigation of the optical properties of complex Cr-based hard coatings and their connection with the compound structure of the coatings is presented. Cr/CrN, Cr/CrN/CrAlN, Cr/CrN/CrTiAlN, and Cr/CrN/CrAlTiN coating structures were deposited through unbalanced magnetron sputtering. Their mechanical properties, especially nanohardness, coefficient of friction, and adhesion, were measured. The structure and composition of the coatings were characterised through SEM, FIB, XPS, and TEM. Their optical properties were investigated by UV-VIS ellipsometry. The optical parameters' phase difference Δ, the amplitude ratio Ψ, the frequency-dependent real (ε1(ω)) and imaginary (ε2(ω)) part of the dielectric function, and the corresponding refractive and extinction indexes n(ω) and k(ω) were measured and modelled via regression analysis implemented using the WVASE© software version 3.686. Satisfactory coincidence was achieved between the measured optical data and the corresponding fitting models. The physical polycrystalline optical constants of the industrial samples were extracted from modelling data with roughness. The analysis of the data showed that ellipsometric characterisation can be used in order to determine the physical properties of Cr-based hard coatings with complex structure and composition, as well as for repeatability control of the deposition process. However, more detailed research is needed to predict the composition based on measured optical properties. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry and ultraviolet-visible (UV-VIS) spectrometry were utilized to study the optical properties of ferroelectric lead lanthanum zirconate titanate (PLZT) films. These films were deposited on platinized silicon [Si(100)/ SiO2/TiO2/Pt(111)] substrates using the chemical solution deposition method. Films were annealed at two different temperatures (650 and 750 °C) using rapid thermal annealing. Shimadzu UV-1800 UV-VIS spectrophotometer with a resolution of 1 nm was used to measure the reflectance data in the spectral range of 300–1000 nm with a step size of 1 nm. The bandgap values were determined from the reflectance spectra using appropriate equations. A J.A. Woollam RC2 small spot spectroscopic ellipsometer was used to obtain the change in amplitude (Ψ) and phase (Δ) of polarized light upon reflection from the film surface. The spectra were recorded in the wavelength range of 210–1500 nm at an incident angle of 65°. Refractive index (n) and extinction coefficient (k) were obtained by fitting the spectra (Ψ, Δ) with the appropriate models. No significant changes were observed in the optical constants of PLZT films annealed at 650 and 750 °C. The optical transparency and the strong absorption in the ultraviolet (UV) region of PLZT films make them an attractive material for optoelectronic and UV sensing applications. [ABSTRACT FROM AUTHOR]

Infrared refractive indices of organic materials are typically resolved through IR ellipsometry. This technique takes advantage of optical interference effects to solve the optical constants. These are the same effects that complicate the analysis of coherent spectroscopy experiments on thin films. Vibrational sum frequency generation is an interface-specific coherent spectroscopy that requires spectral modeling to account for optical interference effects to uncover interfacial molecular responses. Here, we explore the possibility of leveraging incident beam geometries and sample thicknesses to simultaneously obtain the molecular responses and refractive indices. Globally fitting a higher number of spectra with a single set of refractive indices increases the fidelity of the fitted parameters. Finally, we test our method on samples with a range of thicknesses and compare the results to those obtained by IR ellipsometry. [ABSTRACT FROM AUTHOR]

In this work, the spectra of optical constants of epitaxial layers of cadmium telluride near the fundamental absorption edge are studied. For this purpose, ellipsometric measurements of the layers under study were carried out in a vacuum chamber in the temperature range from T = 38–275°C. A numerical algorithm has been developed for solving the inverse ellipsometry problem for the structures under consideration, with the help of which the spectral dependences of the refractive index n(λ) and absorption index k(λ) are determined in the wavelength range from 700 to 1000 nm. The parametric dependences of k(λ, T) in the fundamental absorption region and in the transparency region are presented. The presence of an extended absorption tail in the transparency region was established, presumably associated with imperfections in the crystal structure. [ABSTRACT FROM AUTHOR]

Metal based electroreflective devices (MERDs) have gained wide attention in recent years in the fields of smart windows and automotive glass due to their excellent photo-thermal modulation capability in the visible and near-infrared wavelength bands due to their high reflectivity. However, the high porosity due to the island-like growth of silver particles makes the devices susceptible to electrodeposited film breakage during prolonged energization or bleaching. This will seriously affect the effectiveness and stability of the device. In this paper, it is shown that the problem of Ag electrodeposition film fragmentation can be effectively overcome by replacing dimethyl sulfoxide solvent by N-methylpyrrolidone (NMP). The optical constants during film deposition were tested by the spectroscopic ellipsometry technique, and the porosity was calculated (reduced by 21.6%). The results show that MERDs with NMP as the solvent have more and more dispersed silver deposition sites, which leads to lower porosity of the silver deposited film during the deposition process. In addition, the lower turn-on voltage, greater contrast, longer memory effect, and greater coloring efficiency reveal that they are more promising for energy-saving applications. [ABSTRACT FROM AUTHOR]

In order to model the propagation of light through a sand cloud, it is critical to have accurate data for the optical constants of the sand particles that comprise it. The same holds true for modeling propagation through particles of any type suspended in a medium. Few methods exist, however, to measure these quantities with high accuracy. In this paper, a characterization method based on spectroscopic ellipsometry (SE) that can be applied to a particulate material is presented. In this method, a polished disc of an adhesive compound is prepared, and its optical constants are measured. Next, a mixture of the adhesive and a sand sample is prepared and processed into a polished disc, and SE is performed. By treating the mixture as a Bruggeman effective medium, the optical constants of the particulate material are extracted. For verification of the proposed method, it is first applied to pure silica powder, demonstrating good agreement between measured optical constants and literature values. It is then applied to Arizona road dust, a standard reference material, as well as real desert sand samples. The resulting optical constant data is input into a rigorous scattering model to predict extinction coefficients for various types of sand. Modeling results are compared to spectroscopic measurements on static sand samples, demonstrating good agreement between predicted and measured spectral properties including the presence of a Christiansen feature near a wavelength of 8 µm. [ABSTRACT FROM AUTHOR]

The Ge x Sb 30-x Se 70 : x = 30, 25, 15, 10 glass films were prepared by thermal evaporation technique. The surface morphology of glass films was studied by atomic force microscopy. The samples exhibited surface roughness with a root mean square value falling within the 0.89–1.47 nm range. The optical properties were precisely characterized by spectroscopic ellipsometry in the 4.13–0.77 eV spectral range. The Cody-Lorentz dispersion model was used to fit the data across the entire spectral range and extract the optical functions of glass films. It has been observed that the refractive index, n values rise with increasing energy, reaching a peak, and then experience a subsequent decline. The refractive index values exhibit a rising trend with an increase in Sb content. The optical bandgap, E g opt was found to follow a decreasing pattern with a decrease in Ge content. The refractive index dispersion curve was analyzed using the Wemple and DiDomenico single oscillator model in the lower absorption spectral region. It has been observed the values of oscillator energy, E o, and static refractive index, n 0, exhibit a pattern consistent with that of E g opt , and n, respectively. The optical properties, such as the high-frequency dielectric constant, carrier concentration, plasma frequency, and optical conductivity were analyzed. [ABSTRACT FROM AUTHOR]

As a non-destructive and rapid technique, optical scatterometry has gained widespread use in the measurement of film thickness and optical constants. The recent advances in deep learning have presented new and powerful approaches to the resolution of inverse scattering problems. However, the application of deep-neural-network-assisted optical scatterometry for nanostructures still faces significant challenges, including poor stability, limited functionalities, and high equipment requirements. In this paper, a novel characterization method is proposed, which employs deep-neural-network-assisted ellipsometry to address these challenges. The method processes ellipsometric angles, which are measured by basic ellipsometers, as functional signals. A comprehensive model is developed to profile nano-gratings fabricated by diverse techniques, by incorporating rounded corners, residual layers, and optical constants into an existing model. The stability of the model is enhanced by implementing several measures, including multiple sets of initial values and azimuth-resolved measurements. A simple compensation algorithm is also introduced to improve accuracy without compromising efficiency. Experimental results demonstrate that the proposed method can rapidly and accurately characterize nano-gratings fabricated by various methods, with relative errors of both geometric and optical parameters well controlled under 5 %. Thus, the method holds great promise to serve as an alternative to conventional characterization techniques for in-situ measurement. [ABSTRACT FROM AUTHOR]

In this paper, we show and analyse the results of morphological characterisations of Dy2O3 layer deposited on an n-type GaAs substrate using atomic force microscopy (AFM). For structural measurement, the surface morphology of the elaborated layer was revealed as a nano-conical event. The global experimental ellipsometric results Ψ and Δ versus emission wavelength of the Dy2O3/n-GaAs structure have been presented and discussed. Using these results and a Matlab code in which we assumed the structure had three layers, we have calculated several linear and nonlinear optical constants of the Dy2O3 thin layer. Dysprosium oxide has high optical conductivity and a noticeable increase in nonlinear optical parameters, making it a promising candidate for various applications. This is especially true in the field of optoelectronics. [ABSTRACT FROM AUTHOR]

In this work, we discuss the precision of the effective medium approximation (EMA) model in the data analysis of spectroscopic ellipsometry (SE) for solid materials with micro-rough surfaces by drawing the regime map. The SE parameters ψ (amplitude ratio) and Δ (phase difference) of the EMA model were solved by rigorous coupled-wave analysis. The electromagnetic response of the actual surfaces with micro roughness was simulated by the finite-difference time-domain method, which was validated by the experimental results. The regime maps associated with the SE parameters and optical constants n (refractive index) and k (extinction coefficient) of the EMA model were drawn by a comparison of the actual values with the model values. We find that using EMA to model micro-rough surfaces with high absorption can result in a higher precision of the amplitude ratio and extinction coefficient. The precisions of ψ, Δ, n and k increase as the relative roughness σ/λ (σ: the root mean square roughness, λ: the incident wavelength) decreases. The precision of ψ has an influence on the precision of k and the precision of Δ affects the precision of n. Changing σ alone has little effect on the regime maps of the relative errors of SE parameters and optical constants. A superior advantage of drawing the regime map is that it enables the clear determination as to whether EMA is able to model the rough surfaces or not. [ABSTRACT FROM AUTHOR]

We report new optical constants (refractive index, n, and extinction coefficient, k) for exoplanet haze analogs from 0.3 to 30 µm. The samples were produced in a simulated N2-dominated atmosphere with two different abundance ratios of CO2 and CH4, using the PAMPRE plasma reactor at LATMOS. We find that our haze analogs present a significantly lower extinction coefficient in the optical and near-infrared (NIR) range compared to the seminal data obtained on Titan haze analogs. We confirm the stronger IR absorption expected for hazes produced in a gas mixture with higher CO2 abundances. Given the strong impact of the atmospheric composition on the absorbing power of hazes, these new data should be used to characterize early-Earth and CO2-rich exoplanet atmospheres. The data presented in this paper can be found in the Optical Constants Database. Using ellipsometry or spectrophotometry, the retrieved optical constants are affected by the sensitivity of the measurement and the accuracy of the calculations. A comparative study of both techniques was performed to identify limitations and better understand the discrepancies present in the previous data. For the refractive index n, errors of 1–3% are observed with both optical techniques and the different models, caused by the correlation with the film thickness. We find that UV-visible reflection ellipsometry provides similar n values, regardless of the model used; whereas the Swanepoel method on transmission is more subjected to errors in the UV. In the UV and mid-infrared (MIR), the different calculations lead to rather small errors on k. Larger errors of k arise in the region of weak absorption, where calculations are more sensitive to errors on the refractive index n. [ABSTRACT FROM AUTHOR]

Asphalt pavement possesses the characteristics of strong sunlight absorption, which lead to the aging of asphalt binder. Asphalt aging is one of the leading causes of the performance deterioration in the asphalt pavement, and the appearance of crystalline wax (paraffin wax) during aging has a significant effect on optical properties (absorption and reflection) of the asphalt binder. In this paper, effects of the crystalline wax on optical properties of the asphalt binder were investigated using the spectroscopic ellipsometry (SE) technique, and a new method for the quantification of the crystalline wax in asphalt was also developed. Cold Lake asphalt doped with different contents of n-alkanes (eicosane, triacontane, and tetracontane) were tested by the SE. The results showed that there is a close linear relationship between the optical constants and wax content of the asphalt binder. In addition, with increasing both the chain length of n-alkanes and their content, the reflection intensity of the asphalt binder decreased, and the refractive index and extinction coefficient increased accordingly. On the whole, ellipsometry-based optical testing is a promising method for rapid and non-destructive identification of wax in asphalt. [ABSTRACT FROM AUTHOR]

A pure experiment-based work was conducted to investigate the optical characteristics of a thin absorbing singlelayer copper film at various annealing temperatures. The study also systematically examined the utilization of spectroscopic ellipsometry as an effective tool for fine-tuning the optical constants of thin films, particularly for achieving specific refractive index (n) and extinction coefficient (k) values. The measurement and analysis involved a thermally deposited thin nanosized single-layer copper film on a glass substrate, along with a spectroscopic ellipsometer. [ABSTRACT FROM AUTHOR]

Native defects in semiconductors play an important role in their optoelectronic properties. Nickel oxide (NiO) is one of the few wide-gap p-type oxide semiconductors and its conductivity is believed to be controlled primarily by Ni-vacancy acceptors. Herein, we present a systematic study comparing the optoelectronic properties of stoichiometric NiO, oxygen-rich NiO with Ni vacancies (NiO:VNi), and Ni-rich NiO with O vacancies (NiO:VO). The optical properties were obtained by spectroscopic ellipsometry, while valence band spectra were probed by high-resolution x-ray photoelectron spectroscopy. The experimental results are directly compared to first-principles density functional theory + U calculations. Computational results confirm that gap states are present in both NiO systems with vacancies. Gap states in NiO:Vo are predominantly Ni 3d states, while those in NiO:VNi are composed of both Ni 3d and O 2p states. The absorption spectra of the NiO:VNi sample show significant defect-induced features below 3.0 eV compared to NiO and NiO:VO samples. The increase in sub-gap absorptions in NiO:VNi can be attributed to gap states observed in the electronic density of states. The relation between native vacancy defects and electronic and optical properties of NiO are demonstrated, showing that at similar vacancy concentration, the optical constants of NiO:VNi deviate significantly from those of NiO:VO. Our experimental and computational results reveal that although VNi are effective acceptors in NiO, they also degrade the visible transparency of the material. Hence, for transparent optoelectronic device applications, an optimization of native VNi defects with extrinsic doping is required to simultaneously enhance p-type conductivity and transparency. [ABSTRACT FROM AUTHOR]

The optical constants of a linear chain carbon (LCC) film in the spectral range from 248 to 1100 nm (1.13–5.0 eV with a step of 0.1 eV) were obtained by the Beatty ellipsometric method, and its thickness was determined. The LCC film was deposited on a pre-polished mirror surface of a massive steel sample using the technology of pulsed carbon plasma with ion stimulation. It was found that in the measured range of the spectrum the refractive index of the film varies from 2.35 to 2.73, and the value of k varies from a value close to zero to 1.02. The effective film thickness is determined to be d = 92 ± 2 Å. According to the type of conductivity, the LCC film is a dielectric (Eg= 4.1 eV). A simplified method for determining the band gap of nanosized semiconductor and dielectric films is proposed. [ABSTRACT FROM AUTHOR]

Optical constants n and k of a polycrystalline film of aluminum alloy and 2.54 at % praseodymium were measured at room temperature. Based on these data, optical-conductivity spectra were obtained for a clean and oxidized alloy surface. When analyzing the results of comparing these spectra with the model ones, the electronic characteristics of optical transitions, including the characteristics of surface states of electrons, were obtained. It is shown that the conduction band of an alloy with a clean surface is split to a minimum extent. The oxygen-adsorption heat values on the surface of an Al–2.54 at % Pr alloy film have been calculated. The equilibrium position of the adsorption–desorption processes of an alloy film at room temperature is significantly shifted towards desorption. [ABSTRACT FROM AUTHOR]

The dissolution of zinc oxide is investigated using spectroscopic ellipsometry to investigate its suitability as a platform for biosensing applications. The results indicate that once the ZnO surface has been functionalised, it is suitably protected, and no significant dissolving of the ZnO occurs. The binding kinetics of the SARS-CoV-2 spike protein on aptamer-functionalised zinc oxide surfaces are subsequently investigated. Values are extracted for the refractive index and associated optical constants for both the aptamer layer used and the protein itself. It is shown that upon an initial exposure to the protein, a rapid fluctuation in the surface density is observed. After around 20 min, this effect stabilises, and a fixed increase in the surface density is observed, which itself increases as the concentration of the protein is increased. This technique and setup are demonstrated to have a limit-of-detection down to 1 nanomole (nM) and display a linear response to concentrations up to 100 nM. [ABSTRACT FROM AUTHOR]

The optical properties of TlIn(S0.25Se0.75)2 crystals were studied by ellipsometry measurements. X-ray diffraction pattern presented well-defined peaks associated with monoclinic structure. Energy dependent graphs of various linear optical parameters of the crystal were presented in the 1.25–4.50 eV range. The band gap and Urbach energies of the compound were found as 1.96 and 0.68 eV, respectively, from the analyses of the absorption coefficient. Refractive index spectrum was analyzed considering the single-effective-oscillator model to get oscillator and dispersion energies, zero and high frequency dielectric constants, plasma frequency. Moreover, the nonlinear refractive index, first-order and third-order nonlinear susceptibilities of TlIn(S0.25Se0.75)2 crystal were revealed in the present paper. [ABSTRACT FROM AUTHOR]

The determination of the effective optical constants of metal island films is an essential step towards the practical incorporation of this kind of films in optical coatings. In this work, the optical properties of aluminium island films deposited by electron beam evaporation on quartz substrates are investigated using different approaches employed by three research groups. The effective optical constants of the island films are inferred from optical measurements (spectrophotometry and spectroscopic ellipsometry) using: (i) a parameter-free dispersion model, (ii) a multiple oscillator model based on Gaussian line-shapes and (iii) the  β  distributed oscillator model. All the used approaches provide similar physical insights, i.e., an increase in the effective thickness of the metal island film, a red-shift and broadening of the plasmon resonance and an enhancement of the infrared absorption as the amount of deposited material increases. However, the optimal values of the effective optical constants and thickness significantly depend on the employed model and the experimental data used for data fitting. [ABSTRACT FROM AUTHOR]

In this work, we prepared a nanostructure of TCO in a thin film of tin oxide using the spray pyrolysis method. The different deposition parameters have been set and optimized to prepare the source solution from Tin chloride dihydrate deposited on a cleaned glass substrate. The characterization of the thin layer of pure tin oxide deposited by spraying was achieved. The X-ray diffractometer shows that the tin oxide film is polycrystalline with a tetragonal structure, which consists mainly of orientations (101), (211) and other less intense. Ultra-violet-spectroscopy approved an excellent transparency of the thin layer of pure SnO2 with a transmission of 95 % at 600 nm. The optical gap value of the deposited sample is equal to 3.95 eV. The spectroscopic ellipsometry measurements of the Psi and delta parameters were carried out at various angles of incidence 65°, 70° and 75°. The optical constant of the SnO2 layer was modeled using a B-spline model. The goodness of the ellipsometric fitting was found at an incidence angle of 75°, which indicates a minimum MSE equal to 4.022. The SE characterization results of SnO2 thin film on the glass substrate have shown that the layer thickness, the refractive index and the extinction coefficient are equal to 219.78 nm, 1.41 and 0.123, respectively. The resulting structural and optical parameters confirmed that a thin SnO2 layer was formed. This layer showed a wide bandwidth and high transparency of a type of TCO semiconductor, which can be used as an anti-reflective layer in solar cell devices. [ABSTRACT FROM AUTHOR]

The optical properties and electronic characteristics of x-ray amorphous and polycrystalline Al4Sm alloy films obtained by vacuum thermal evaporation were studied. The optical constants were measured by the Beatty ellipsometry method in the range 0.248–7.002 μm. The dispersion dependences of the light conductivity σ, reflectivity R, imaginary and real parts of the dielectric permittivity ε1 and ε2, and characteristic electron energy loss functions Im(ε)–1 were calculated from the spectral dependences of the optical constants. The crystal structure of the alloys was shown to affect features of their optical spectra. The electronic characteristics of these alloys were calculated from measurements in the IR spectral region using the two-band conductivity model. [ABSTRACT FROM AUTHOR]

The optical characterization of gadolinium fluoride (GdF3) films is performed in a wide spectral range using heterogeneous data-processing methods (the ellipsometric and spectrophotometric measurements for five samples with thicknesses ranging from 20 to 600 nm are processed simultaneously). The main result of the characterization is the optical constants of GdF3 in the range from far infrared to vacuum ultraviolet, both in the form of a table and in the form of dispersion parameters of the universal dispersion model (UDM). Such reliable data in such a broad spectral range have not been published so far. The GdF3 films exhibit several defects related to the porous polycrystalline structure, namely, surface roughness and a refractive index profile, which complicate the optical characterization. The main complication arises from the volatile adsorbed components, which can partially fill the pores. The presented optical method is based on the application of the UDM for the description of the optical response of GdF3 films with partially filled pores. Using this dispersion model, it is possible to effectively separate the optical response of the host material from the response of the adsorbed components. Several recently published structural and dispersion models are used for optical characterization for the first time. For example, a model of inhomogeneous rough films based on Rayleigh–Rice theory or asymmetric peak approximation with a Voigt profile for the phonon spectra of polycrystalline materials. [ABSTRACT FROM AUTHOR]

In this work, the optical properties of niobium pentoxide ( Nb 2 O 5 ) films were extensively studied across a wide spectral range using heterogeneous data-processing methods, combining ellipsometric and spectrophotometric measurements for five samples with thicknesses between 20 and 250 nm. This study primarily determined the optical constants of Nb 2 O 5 from the far infrared to the vacuum ultraviolet, presenting these constants as dispersion parameters using the universal dispersion model to describe valence electron excitations in ultraviolet region as well as phonon vibrations in infrared region. These comprehensive and reliable data across such a broad spectral range are unprecedented. Secondly, presented optical characterization proofs that Nb 2 O 5 films can be grown without defects such as surface roughness, porosity, or inhomogeneity. This fact, together with its high refractive index, makes Nb 2 O 5 a promising material for optical applications. • Optical constants of Nb2O5 films determined in unprecedented spectral range. • Optical characterization using multi-instrument and multi-sample method. • Physically consistent universal dispersion model employed. • Phonons described using asymmetric Voigt profiles. • Electronic excitations modeled using truncated Lorentz and Urbach tail models. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterostructures pave the way to achieve the desired material properties for a variety of applications. In this way, new scientific and industrial challenges and fundamental questions arise. One of them is whether vdW materials preserve their original optical response when assembled in a heterostructure. Here, we resolve this issue for four exemplary monolayer heterostructures: MoS2/Gr, MoS2/hBN, WS2/Gr, and WS2/hBN. Through joint Raman, ellipsometry, and reflectance spectroscopies, we discovered that heterostructures alter MoS2 and WS2 optical constants. Furthermore, despite the similarity of MoS2 and WS2 monolayers, their behavior in heterostructures is markedly different. While MoS2 has large changes, particularly above 3 eV, WS2 experiences modest changes in optical constants. We also detected a transformation from dark into bright exciton for MoS2/Gr heterostructure. In summary, our findings provide clear evidence that the optical response of heterostructures is not the sum of optical properties of its constituents. [ABSTRACT FROM AUTHOR]

Nanocrystalline graphite (NCG) layers represent a good alternative to graphene for the development of various applications, using large area, complementary metal-oxide semiconductor (CMOS) compatible technologies. A comprehensive analysis of the physical properties of NCG layers—grown for different time periods via plasma-enhanced chemical vapour deposition (PECVD)—was conducted. The correlation between measured properties (thickness, optical constants, Raman response, electrical performance, and surface morphology) and growth time was established to further develop various functional structures. All thin films show an increased grain size and improved crystalline structure, with better electrical properties, as the plasma growth time is increased. Moreover, the spectroscopic ellipsometry investigations of their thickness and optical constants, together with the surface roughness extracted from the atomic force microscopy examinations and the electrical properties resulting from Hall measurements, point out the transition from nucleation to three-dimensional growth in the PECVD process around the five-minute mark. [ABSTRACT FROM AUTHOR]

Terbium gallium garnet (TGG – Tb 3 Ga 5 O 12 ) single crystal was optically characterized using the multi-sample and multi-instrument method across a wide spectral range with the help of the universal dispersion model. The obtained optical constants cover the spectral range from the far-IR region (25 cm − 1 ) to the vacuum-UV region (10.3 eV). The applied dispersion model includes all elementary absorption processes occurring within the spectral range that affect the dielectric response, including phonons and valence electron excitations. The primary objective was to accurately determine the optical constants with the highest possible precision. The optical results were compared with ab initio density functional theory calculations to gain insight into the nature of the absorption edge and the distribution of the f-electron excitations. • High resolution optical constants of terbium gallium garnet in wide spectral range. • Asymmetric absorption profile of coupled TO phonons. • Influence of isotopes on the shape of TO phonon absorption structures. • Excitonic nature of the fundamental absorption edge. • Density functional theory calculation of systems with highly correlated electrons. [ABSTRACT FROM AUTHOR]

The structural and optical properties of CdS window layer at different thicknesses in the range of (100-300 nm) deposited on pre-cleaned glass substrates (CdS/glasses) via the thermal evaporation process are studied in the current work. The structural analysis is done using Rietveld refinement and atomic pressure microscope techniques. The films of CdS/glass showcase a wurtzite behavior. XRD and AFM tests are confirmed that the structural parameters improve as the thickness of the CdS-layer increases. The optical constants (the refractive index n, the extinction coefficient, k and the bandgap energy values are estimated from spectroscopic ellipsometry (SE) via the construction of an optical model. The refractive index of the CdS/glass films increases with the increase of CdS-layer thickness. This, in turn, is due to the rise of the size of the crystal in the thin layers. It is also found that as the thickness of the CdS-layer rises, so does the overall behavior of the extinction coefficient. Additionally, the bandgap energy of the direct transition decreases from 2.45 eV (d=100 nm) to 2.25 eV (d=300 nm). The dark and illumination I-V photovoltaic characteristics of fabricated devices are explored by depositing a p-CdTe thin layer (500 nm) over varying thicknesses of CdS thin films (100- 300 nm) prepared on glass substrates (2 mm) and thus, the Ni/n-CdS/i-AgSe/p-CdTe/Pt heterojunction has been successfully fabricated with an AgSe buffer layer deposited directly on the p-CdTe absorber laryer. The n-CdS window layer is deposited on i-AgSe buffer layer. In dark conditions, based on the dependence of the forward and reverse current-voltage, the essential behavior related to the fabricated diode has been determined. As well, in the illumination case, the open-circuit voltage, the short-circuit current, the fill factor, the power conversion efficiency, (PCE), photoresponsivity, quantum efficiency, dependence of generated photocurrent on the light intensity, dependence of the generated photocurrent on wavelength (λ)for the studied solar cell are computed and discussed. [ABSTRACT FROM AUTHOR]

Poly‐ether‐ether‐ketone (PEEK) is a widely used and versatile polymer. Here, we use ellipsometry to determine the wavelength‐dependent optical properties of PEEK before and after the surface is modified by plasma immersion ion implantation (PIII), a technique that renders the surface hydrophilic and bio‐active. Lorentz and Gaussian oscillator models are used to fit the data for extraction of the optical constants and the dielectric function. The effect of PIII, even for short treatment times, changes the optical properties of PEEK, indicative of an amorphisation of the initial semicrystalline structure that broadens the electronic density of states distribution. The progressive changes in the optical properties with treatment time allow assessment of colour changes and estimation of ion dose in the PIII process. [ABSTRACT FROM AUTHOR]

When comparing the simulated and experimental optical conductivity, the electronic structure of the aluminum film and powder at room temperature was studied. The positions and occupation of their surface states by electrons are determined. It has been established that the dispersion of aluminum leads to a sharp increase in the filling of its surface states with electrons. Since adsorption processes are most clearly manifested in a change in the characteristics of surface states, such states can be considered as an adsorption center. Thus, we can conclude that the dispersion of aluminum leads to an increase in the number of its adsorption centers. [ABSTRACT FROM AUTHOR]

Ellipsometry measurements were taken on single-crystalline Ni(100) at various temperatures between 77 and 770 K. DC conductivity and resistivity are extracted from the model optical constants and their temperature dependence is discussed. The authors find only qualitative agreement in the general trend of the resistivity measured by ellipsometry and electrical measurements. The temperature dependence of the main absorption peak at 4.8 eV indicates that the interband transitions are scattered by magnons with an effective energy of about 53 meV. The width of the main absorption peak reduces by 0.38 eV as the temperature rises, which is interpreted as the ferromagnetic exchange energy at the L-point. The small absorption peak at 1.5 eV is prominent only in the ferromagnetic phase and almost disappears in the paramagnetic phase. This peculiarity is explained by assigning the peak to K 3 ↓ → K 2 ↓ transitions, which accounts for the decrease of the magnitude of the peak and its constant energy. [ABSTRACT FROM AUTHOR]

Optical constants n and k of polycrystalline films of aluminum and Al–4.45 at % La alloy have been measured at room temperature. The optical conductivity spectra for the clean and oxidized surfaces of the above systems have been obtained based on these data. When analyzing the results of comparison of these spectra with the model ones, the electronic characteristics of optical transitions, including the characteristics of the surface states of electrons, have been obtained. It has been shown that the conduction band of these systems was multiply split. It has been demonstrated that the center of gravity of the contribution to the optical-conductivity spectrum from the surface states of electrons for the alloy was shifted towards lower energy values, as compared with a similar contribution for the aluminum film. The value of the heat of oxygen adsorption on the surface of aluminum and alloy has been calculated. It has been established that the equilibrium position of the adsorption–desorption processes of above-mentioned systems at room temperature is shifted towards desorption, while the heat of oxygen desorption on the surface of the Al–4.45 at % La alloy is significantly lower than the desorption heat for the aluminum film. [ABSTRACT FROM AUTHOR]

This paper reports thickness-dependent structural, morphological, optical, and electrical conduction mechanism of room temperature electron beam evaporated 2D WSe2 thin films on glass substrate. The thickness of the WSe2 films was varied from 100 to 400 nm. XRD results showed the fact that the WSe2 films are crystallized in a hexagonal structure. The nanostructure nature is verified from morphological studies. It was found that the microstrain decreases, while the crystallite size rises as the thickness of WSe2 film increases. The thickness-dependent optical constants and energy bandgap was studied using spectroscopic ellipsometry (SE). The refractive index and extinction coefficient dispersion curves of WSe2 film with various thicknesses display two strong absorption peaks A and B below 800 nm at 580 nm and 770 nm, which are belong to excitonic absorption features. Further, the results illustrate that the optical constants and optical bandgap of thin WSe2 films are strongly correlated with the film thickness. In addition, the electrical conduction mechanism in different temperature regimes is explained in terms of Arrhenius activated thermal conduction, Mott's variable-range hopping (VRH), and Seto's grain boundary effect models. The most interesting finding is that the film exhibits wide absorption coefficient (106 cm−1) and energy gap value closely matches the solar spectrum, making it an excellent candidate for photovoltaic materials as an absorber layer. [ABSTRACT FROM AUTHOR]

A manual null ellipsometer is constructed and used to determine the optical constants of zinc and cadmium of different surface roughness at the wavelength 632.8 nm, angle of incidence 45° and room temperature. The studied samples are polycrystalline sheets of thickness ~ 0.05 mm and surface area 30 mm x 30 mm. The samples were mechanically polished using diamond paste of different grain sizes. The final stage of polishing for the samples was with pastes of grain size 0.5 μm, 2.5 μm, 5 μm, 10 μm and 14 μm. The ellipsometric parameters ψ and Δ were obtained and were used to calculate the optical constants n (refractive index) and k (extinction coefficient). It was found that as the roughness is increased, the refractive index n increases while the extinction coefficient k decreases. The used optical arrangement for ellipsometric measurements is presented and the procedure for extracting the results is explained. The uncertainty in the results is calculated and included in the results.

Spectra of the optical constants n and k of a substance are often deduced from spectroscopic measurements, performed on a thick and homogeneous sample, and from a model used to simulate these measurements. Spectra obtained for n and k using the ellipsometric method generally produce polarized reflectance simulations in strong agreement with the experimental measurements, but they sometimes introduce significant discrepancies over limited spectral ranges, whereas spectra of n and k obtained with the single-angle reflectance method require a perfectly smooth sample surface to be viable. This paper presents an alternative method to calculate n and k. The method exploits both ellipsometric measurements and s -polarized specular reflectance measurements, and compensates for potential surface scattering effects with the introduction of a specularity factor. It is applicable to bulk samples having either a smooth or a rough surface. It provides spectral optical constants that are consistent with s -polarized reflectance measurements. Demonstrations are performed in the infrared region using a glass slide (smooth surface) and a pellet of compressed ammonium sulfate powder (rough surface). [ABSTRACT FROM AUTHOR]

The optical properties of unoxidized surfaces of the praseodymium and neodymium polycrystalline films in the spectral range of 0.4–2.6 μm are studied. Optical constants are measured using the Beattie ellipsometric method. The dispersion dependences of light conductivity σ, reflectivity R, the imaginary and real parts of the dielectric constant (ε1 and ε2, respectively), and the Im(ε)–1 function of characteristic electron energy losses are calculated using the obtained optical constants. The optical properties of both films and liquid metals studied earlier are given. Using the results of optical measurements in the infrared spectral region, the electronic characteristics of praseodymium and neodymium in the solid thin-film and liquid states are calculated by the two-band conductivity model. [ABSTRACT FROM AUTHOR]

CsPbX3 (X = Cl, Br, or I) perovskite thin films can be fabricated by vacuum evaporation (VE) with high reproducibility and good film-forming ability. To design optical devices based on CsPbX3 thin films, precise optical constants are required. As only a few optical and dielectric properties of perovskites obtained by VE have been reported, we have comprehensively studied the complex reflective index and complex dielectric function of CsPbBr3 perovskite VE films. Spectroscopic ellipsometry combined with x-ray diffraction and scanning electron microscopy revealed that the three-oscillator model precisely describes the optical constants. Therefore, the wavelength-dependent optical constants of a material can be empirically determined. Time-resolved photoluminescence of a designed CsPbBr3-light-emitting device with a Fabry–Perot cavity and agreement of its dielectric properties with reported data confirmed the existence of a microcavity effect and accurately predicted the electric field intensity distribution and cavity length. This methodology also enables the composition of perovskite to be monitored, which contains a fraction that is desirable for optimizing the performance of optical electronics. [ABSTRACT FROM AUTHOR]

Titanium (Ti) doped tungsten oxide (WO3) thin films were grown by co-sputter deposition of W and Ti metal targets. The sputtering powers to the W and Ti were kept constant at 100W and 50 W, respectively, while varying the growth temperature (Ts) in the range of 25-400 °C. The structural quality of Ti-doped WO3 films is dependent on Ts. Ti-doped WO3 films grown at Ts<400 °C were amorphous. A temperature of 400 °C is critical to promote the structural order and formation of monoclinic, nanocrystalline films. The optical constants and their dispersion profiles determined from spectroscopic ellipsometry indicate that there is no significant inter-diffusion at the film-substrate interface for W-Ti oxide film growth of ∼40 nm. The index refraction (n) at λ=550 nm varies in the range of 2.15-2.40 with a gradual increase in Ts. Lorentz-Lorenz analysis (n(λ)=550 nm) of the data indicates the gradual improvement in the packing density coupled with structural transformation accounts for the observed optical quality of the Ti-doped WO3 films as a function of Ts. A correlation between the growth conditions and optical constants is discussed. [ABSTRACT FROM AUTHOR]

This work utilized the optical properties of indium tin oxide/silver/indium tin oxide electrodes to set up the fitting range for spectroscopic ellipsometry (SE) analysis. Then, the SE fitting on the thickness and optical constants of each layer in several separate stages was investigated. In this way, the results suggest that the SE fitting can be able to converge rapidly and obtain the precise thickness of each layer. Experiment analysis shows that when the silver layer thickness was 8.5–11.5 nm, the sheet resistance of the uniform electrodes was < 8.5 Ω/sq, while the average transmittances were > 82.0% in the visible light region; the related Haacke indexes were > 22.0 × 10−3 Ω−1. For photovoltaic application, when the silver layer thickness was 7.5–8.5 nm, the sheet resistance of the three-layer electrodes was < 9.0 Ω/sq, while their average transmittance was > 77.5%; the related Haacke indexes were > 9.0 × 10−3 Ω−1. Comparing the SE results with experimental measurements, it is concluded that the uniformity of the silver layer and the stability of the sputtering system were the major factors affecting the optoelectronic performance of the three-layer electrodes. [ABSTRACT FROM AUTHOR]

Titanium-vanadium dioxide or TixV1−xO2 films for 0 ≤ x ≤ 1 were examined using ellipsometry, and their optical constants (n and k) at visible and near-infrared wavelengths were determined at temperatures (T) below, at, and above the semiconductive-to-metallic phase transition (SMT) temperature (TSM). Ellipsometric analysis was performed for each x at each T using a wavelength dispersion model, i.e., a combination of Lorentz oscillators and a Drude free electron model. The ellipsometric analyses provided information on the electronic band transition caused by the SMT and the influence of cationic replacement (Ti↔V) on the SMT. The results revealed that when x ≤ 0.05, close to the SMT, the energy gap of the interband transition O2p→V3d varied from ≈3.5 eV to ≈3.1 eV, and the quantity of electrons in the interband transition decreased by half. In addition, the energy gap monotonically increased to 4.2 eV when x was increased to 1. Moreover, the energy gap of the split V3d intraband transition varied from ≈1.4 eV to zero, and the quantity of electrons in the intraband transition increased by a factor of four. Furthermore, when x ≥ 0.2, close to the SMT, the energy gap of the intraband transition varied from ≈1.4 eV to a constant positive value, with the generation of a small number of conductive electrons, depending on x. [ABSTRACT FROM AUTHOR]

Nanostructured Fe:SnO2 thin films were deposited on glass substrates through sol–gel spin coating method. Films were synthesized with different iron quantities including 0%, 4%, 8% and 12% (wt.%). The effects of Fe concentration on optical properties of films were investigated by spectroscopic ellipsometry (SE) technique. SE measured (Ψ , Δ) parameters for films in the wavelength range between 300 nm to 800 nm. Optical properties including the refractive index, extinction coefficient, transmittance, dielectric constants and optical conductivity were determined by fitting the SE measured (Ψ , Δ) parameters and data obtained from the optical model-based analysis. Results showed that the transmittance values increase by increment of Fe concentration from 0% to 12%. The bandgap energy ( E g) of prepared thin films was also calculated. E g values were between 3.44 and 3.58 eV. Dispersion parameters including the high frequency dielectric constant ( ε ∞) and the ratio of free carrier concentration to effective mass (N/m ∗) were then obtained for the prepared films. [ABSTRACT FROM AUTHOR]

Based on in situ and ex situ ellipsometric measurements, the spectral dependences of the temperature sensitivity of the optical constants Hg1 –xCdхTe—dn(λ) and dk(λ) have been found for a series of samples of different compositions in the range from 0.160 to 0.327. The experiments were performed during cooling of the grown samples in a vacuum chamber. It has been found that the obtained dn and dk dependences can be well approximated by the sum of three Lorentz oscillators with the addition of the dispersion terms of the Cauchy formula. A parametric model that describes the sensitivities dn(λ) and dk(λ) for an arbitrary composition x in the specified range near the growth temperature has been proposed. Ex situ temperature measurements performed near room temperature correlate with the data of the high-temperature measurements. The results obtained are relevant for the development of ellipsometric control methods in situ of Hg1 –xCdхTe layer growth processes. [ABSTRACT FROM AUTHOR]

A parametric model describing the spectra of optical constants n(λ) and k(λ) of a Hg1 –xCdxTe (MCT) solid solution for the x values in the range from 0.2 to 0.4 is developed. This model is based on empirical data measured in situ during the epitaxial growth of solid-solution layers. Several versions of application of the obtained model for in situ real-time determination of the MCT composition have been considered. A technique for determining the composition using spectral ellipsometric measurements is proposed, which ensures the error of no more than δx = ±0.0035. [ABSTRACT FROM AUTHOR]

In the present research paper, thin films of antimony trisulfide (Sb2S3) were successfully deposited on glass substrates. The effect of thickness on the structural and optical properties of antimony trisulfide (Sb2S3) thin films is studied. The optical constants (n, k) and film thicknesses of Sb2S3 thin films were obtained by fitting the ellipsometric parameters (and) data using three-layer model systems in the wavelength range of 400-1800 nm. It is found that the refractive index n increases with an increase of the film thickness. The structural investigations are performed by Scanning electron microscopy SEM (the Grain size increased with the film thickness). We demonstrate generalized ellipsometry for precise measurement of the principal indices of refraction and the extinction coefficients. [ABSTRACT FROM AUTHOR]

Infrared reflectance analysis is facilitated via the comparison of spectra recorded in situ to a databank of actual or synthetic infrared reflectance spectra. It has recently been shown that reference spectra corresponding to the many different morphological forms of the same chemical can be generated synthetically using the imaginary, k, and real, n, components of the complex refractive index, n=n+ik. One method to obtain the n and k vectors is infrared ellipsometry, which measures the changes in amplitude, tan Ψ, and phase, Δ, of polarized light reflected from the sample both as a function of wavenumber and angle of incidence. The method requires specularly reflected light, so best results are usually obtained with polished planar samples of large surface area. Due to the difficulties of obtaining such samples, however, we investigate the possibility of pressing powders of neat materials and obtaining the corresponding optical constants from the pellets. In this paper, variability in the sample pellet and preparation method is investigated, as is variability in the fitting procedure for the derived optical constants. The n/k vectors are derived from the measured ellipsometric parameters, tan ψ and Δ, as they are fit by an oscillator model which yield n(ν) and k(ν) vectors as a function of wavenumber, ν. Construction of the oscillator model is not automatic and depends on significant input from the analyst as well as the sample's physical characteristics. For pellet pressing, the experimental variability was found to be minimized for size-selected powdered samples as gauged by the minimal variance in ψ and Δ for three different pellets; similarly, the analytical precision for multiple measurements of the same pellet was also quite good, suggesting that a pressed pellet is a viable sample preparation method. Experimental variabilities were comparatively small; the greatest variability came in the analytic fitting procedure with differences in the k-peak values up to 10% for only the sharpest bands arising from four different fits to the same data set. The final ellipsometric n/k data are compared to literature values obtained from crystalline ammonium sulfate ((NH4)2SO4) samples as well as single-angle reflectance measurements that also used pressed pellets. Comparison with the previous literature values shows generally good agreement, although larger k-values are observed for the independent sets of data derived from pressed pellets. These data are suggested as an improved set of optical constants for (NH4)2SO4. [ABSTRACT FROM AUTHOR]