Optical Constants Of Thin Films Research Articles

Terahertz characterization of nano-scale high-entropy alloy films and their high-contrast grating applications

We investigated the optical constants of thin films of the Nb25Mo25Ta25W25 alloy, which belongs to high-entropy alloys (HEAs), with a transmission terahertz (THz) measurement system and discovered that the refractive index, extinction coefficient, and conductivity of the HEA thin film measured in the range of 0.3–1.0 THz all increased as the thickness of the thin film increased (the thickness was maintained in the range between 10 and 40 nm). According to the experimental results, this alloy with a high refractive index is suitable for producing high-contrast gratings (HCGs). The principle behind achieving a high contrast with a high-reflection HEA grating is to harness the confined plasmonic energy within the grating, thereby enhancing the localized plasmonic energy within the grating. This work elucidates that we can not only fabricate THz components by controlling the thickness of the thin film but also utilize the high refractive index of this material to create HCGs.

Spectroscopic Ellipsometry: Advancements, Applications and Future Prospects in Optical Characterization

Spectroscopic ellipsometry (SE), a non-invasive optical technique, is a powerful tool for characterizing surfaces, interfaces, and thin films. By analyzing the change in the polarization state of light upon reflection or transmission through a sample, ellipsometry provides essential parameters such as thin film thickness (t) and optical constants (n, k). This review article discusses the principles of ellipsometry, including the measurement of key values ∆ and Ψ, and the complex quantity ρ. The article also presents the Fresnel equations for s and p polarizations and the importance of oblique angles of incidence in ellipsometry. Data analysis in ellipsometry is explored, including the determination of bandgap and data referencing the electrical properties of materials. The article emphasizes the importance of choosing the appropriate models to fit ellipsometric data accurately, with examples of the Cauchy and Lorentz models. Additionally, the Kramers–Kronig relations are introduced, illustrating the connection between real and imaginary components of optical constants. The review underscores the significance of ellipsometry as a non-destructive and versatile technique for material characterization across a wide range of applications.

Nested Sampling aided determination of tantalum optical constants in the EUV spectral range.

We report on determining the optical constants of Ta in the sub-extreme ultraviolet (EUV) spectral range 5.0-24.0 nm from the angle-dependent reflectance (ADR) measured using monochromatized synchrotron radiation. Two sputtered samples with differing thicknesses were investigated. Complementarily x-ray reflectance was measured at shorter wavelengths and evaluated by Fourier transform to facilitate an unambiguous selection of a model for the data evaluation based on an inverse solution of the Fresnel's equations for a layered system. Bayesian inferences coupled with a Nested Sampling (NS) algorithm were utilized to derive the optical constants with their corresponding uncertainties. This report further emphasizes the applicability of an acclaimed NS algorithm on a high-dimensional inverse problem. We explore the possibility of addressing the correlations between the optical constants of thin films and their structural parameters based on other established studies.

Determination of optical constants of thin films in the EUV.

The determination of fundamental optical parameters is essential for the development of new optical elements such as mirrors, gratings, or photomasks. Especially in the extreme ultraviolet (EUV) and soft x-ray spectral range, the existing databases for the refractive indices of many materials and compositions are insufficient or are a mixture of experimentally measured and calculated values from atomic scattering factors. Since the physical properties of bulk materials and thin films with thicknesses in the nanometer range are not identical, measurements need to be performed on thin layers. In this study we demonstrate how optical constants of various thin film samples on a bulk substrate can be determined from reflection measurements in the EUV photon energy range from 62 eV to 124 eV. Thin films with thickness of 20 nm to 50 nm of pure Mo, Ni, Pt, Ru, Ta, and Te and different compositions of NixAlx, PtTe, PtxMo, RuxTax, Ru3Re, Ru2W, and TaTeN were prepared by DC magnetron sputtering and measured using EUV reflectometry. The determination optical constants of the different materials are discussed and compared to existing tabulated values.

Computer simulation of key structural parameters for enhanced infrared absorption with Au nano-array

The optical constants of thin films with nanoscale structures, such as metamaterials and nanostructured films used in surface enhanced infrared absorption (SEIRA), are represented by effective medium approximation (EMA). In a representative EMA, the effective permittivity is determined by parameters such as the volume filling factor (F). In a metal square column array modeled on an evaporated film, the effective permittivity is determined by the gap size/particle size ratio (f). However, f is also expressed as a function of F. For this study, we simulated the SEIRA spectrum using a model in which f and F were varied independently to investigate which was the most important parameter in the square column array. The results showed all the simulations performed, results showed that the gap size/particle size ratio (f) is an important parameter for the increase in SEIRA in the square column array. This study has led to new discoveries that support elucidation of the SEIRA enhancement mechanism.

Determination of optical constants of thin films in the EUV

Determination of optical constants of thin films in the EUV

Influence of Nitrogen on the Luminescence Properties of Ce-Doped SiOxNy

We report wideband photoluminescent emission from cerium-doped silicon oxynitride (Ce-doped SiOxNy) thin films deposited using electron cyclotron resonance plasma enhanced chemical-vapor deposition (ECR-PECVD). The in situ doping with Cerium (Ce) was performed using a volatile metal organic powder, (Ce[tmhd]4). Oxygen was gradually substituted by nitrogen to produce SiOxNy thin films with varying nitrogen to oxygen ratio, to explore the effect of nitrogen on the photoluminescence (PL) of the thin films. Thin film composition and optical constants were determined using Rutherford back scattering and ellipsometry techniques, respectively. Samples subjected to post-deposition thermal annealing yielded considerably stronger blue/white PL emission than as-deposited ones, due to the formation of Ce-containing clusters at a temperature of 1000 °C and above. X-ray diffraction (XRD) revealed no crystalline structure in samples annealed at elevated temperatures. The optimum layer composition and annealing condition to produce SiOxNy thin films with maximized Ce3+ emission was determined. Besides, hydrogen fluoride etching along with hydrogen passivation demonstrated the enhancement of the PL emission of the thin films.

Artificial bee colony algorithm: a novel strategy for optical constants and thin film thickness extraction using only optical transmittance spectra for photovoltaic applications

An effective approach to determine thin film thickness (d) and optical constants (n,k,α) from transmittance spectrum with interference fringes is proposed. The developed strategy is based on applying the artificial bee colony (ABC) algorithm and Cauchy dispersion model. The accuracy test of this method has been assessed by using simulated and real tests. Simulated test is used to check the ability of ABC algorithm to determine the parameters of simulated transmittance spectra. Real test deals with the investigation of the determination approach on experimental measured transmittance spectra. Those spectra were measured from six elaborated samples of amorphous hydrogenated silicon (a-Si:H) thin films with different thicknesses, which will be used as an eco-friendly layer for solar cell applications. The obtained results noticeably show the high effectiveness of the developed strategy to accurately determine the thin film thickness and optical constants.

Multi-layer Laser Mirrors for Optical Sensors Deposited by Electron Beam Deposition and Ion Assisted Electron Beam Deposition

High reflectivity and low loss mirrors are very much essential for state-of art sensors like Ring Laser Gyroscopes widely used for navigation of moving platforms. Surface scattering is the main source of loss for the Laser mirrors of high reflectivity. Surface scattering also lead to coupling of back reflected light leading to dead band of optical sensors at low input rotation. Super polished glass substrates have been prepared from low expansion glass ceramic material. Surface roughness is achieved about 3-5Å (RMS value) for the ceramic glass substrates prior to thin film coating. The substrates are deposited with 41 alternative layers of SiO2 and Ta2O5 of Quarter-Wave optical thickness with Electron Beam Deposition (EBD) technique. Ion beam Assisted Electron Beam Deposition (IAEBD) is used for another batch of substrates to coat identical stack of layers on glass substrates of the same surface quality. The key process parameters of both the coating processes are presented. The optical constants of the films are evaluated with spectroscopic Ellipsometer from 400nm to 1600nm. Total Integrated Scattering is estimated from the achieved surface finishing of mirrors deposited. The multi-layer coatings are characterized with UV-Vis-IR Spectrophotometer and Cavity Ring Down(CRD) loss meter. The quantitative optical loss of the mirrors is measured at 45o angle of incidence with CRD loss meter. The merits of ion assisted EB process over simple EB coating processes are evaluated against optical constants of thin films and performances of mirrors. Fitness of the processes for realizing Laser mirrors for optical sensors at 632.8nm is evaluated.

Mesoporous copper tin sulphide quantum dots as photoanode materials for efficient dye- sensitized solar cell

In this work, we have synthesized polyethylene glycol capped copper tin sulphide (CTS/PEG) quantum dot thin films by Successive Ionic Layer Adsorption and Reaction (SILAR) technique. The effect of varying PEG content on the structural, optical, morphological and electrical properties of CTS/PEG was investigated. All the samples were crystalline, matching well with tetragonal CTS corresponding to JCPDS 01−089-4714, with high and constant transmittance. The thin film thickness, roughness parameters and optical constants were determined from ellipsometric analysis. The thin film samples were found to be porous with the pore size and particle size decreasing with increasing PEG content. Conductivity and mobility of the charge carriers enhanced with increasing PEG content. Owing to porous nature of CTS/PEG quantum dot thin films with high bandgap, high conductivity, high mobility and low refractive index, these thin films can be effectively used as photoanodes for dye sensitized solar cells.

Electrochromic Behavior and Phase Transformation in Li4+xTi5O12 upon Lithium-Ion Deintercalation/Intercalation.

The impact of phase transformation from spinel-structured Li4Ti5O12 to rocksalt-type Li7Ti5O12 on the electrochromic properties of the material is studied. Thin films of Li4Ti5O12 are deposited on platinum-coated substrates using radio-frequency-ion beam sputtering. In situ and ex situ optical spectroscopy (in reflectance geometry) is performed along with electrochemical characterization. In situ measurements demonstrate the reversible electrochromic behavior of the deposited thin films and the effect of the change of lithium content on the reflectance spectrum. Ex situ measurements quantify the optical constants of thin films for different charge states by modeling the reflectance spectrum with a Clausius-Mossotti relation. The model reveals the presence of one or two dominant resonant frequencies in the case of Li4Ti5O12 or Li7Ti5O12, respectively, in the UV/visible/NIR region of light. The single strong resonance in the case of Li4Ti5O12 is assigned to transition from O 2p to Ti t2g, that is, across the band gap, whereas for the Li7Ti5O12 phase, the two resonances correspond to the electronic transitions from O 2p to empty Ti t2g and from filled Ti t2g to empty Ti eg. The concentration dependence of the derived dielectric constants points out a fast lithium ion transport through the grain boundaries, thereby segregating a conductive lithium-rich phase at the grain boundaries. This increases the electronic conductivity of the thin films in the initial stages of intercalation and explains the debated mechanism of the fast discharge/charge capability of Li4Ti5O12 electrodes.

Validation of thin film TiO2 optical constants by reflectometry and ellipsometry in the VUV spectral range

Optical constants of thin films in the vacuum ultraviolet spectral range are often not precisely known, since not only the experimental determination is difficult, but also the results depend on the sample preparation. We compared measurements in the wavelength interval between 130 nm and 226 nm using reflectometry and ellipsometry with particular regard to their respective uncertainty budgets. Since for both methods a numerical analysis is required to obtain the optical constants from the measured data, particular attention was paid to the error propagation through the calculation routines, and the uncertainties introduced by the numerical methods and models themselves. The measurement methods were applied to a thin layer of 6 nm titania (TiO2) on a silicon substrate. The result is used to validate our method, and to identify further analytical requirements.

Stress and optical constants in thin films of BaF2-PrF3: A potential Th-free infrared low-index evaporation material

Although PrF3 can be regarded as a potential infrared low-index evaporation material used in infrared antireflection to substitute for radioactive ThF4 because its thin films have a good transparency, the lower refractive index n and extinction coefficient k in the spectral range of thermal infrared, the greater tensile stress emerging in its layers will deteriorate the reliability and durability of antireflection coatings. In our investigation, BaF2-PrF3 thin films were deposited using electron beam evaporation from the sintered pellets of PrF3 admixed with BaF2. Stress in thin films was calculated from Stoney’s equation on the basis of measuring the changes of radius of curvature of thin silicon strips. The stoichiometry of thin films was determined using the energy dispersive X-ray analysis (EDX). The optical constants of thin films were determined by fitting the measured spectral transmittance curves using Lorentz oscillators as a dispersion model. It can be observed that stress in BaF2-PrF3 thin films is obviously reduced with the increasing of the concentration of BaF2 in thin films and the sintered pellets. Moreover, it was also demonstrated that incorporation of BaF2 into PrF3 can reduce the refractive index of thin films, although BaF2-PrF3 thin films have a greater dispersion than that of PrF3 thin films. In addition, the lower value of extinction coefficient is also presented in thin films, like those of rare-earth fluorides.

Herramienta de software para determinar constantes ópticas en celdas solares tipo película delgada

En este trabajo se desarrolló una herramienta de software que permite determinar las propiedades ópticas de materiales semiconductores, esta herramienta es de utilidad para investigadores que trabajan en la caracterización de películas delgadas semiconductoras. El software calcula las constantes ópticas: índice de refracción (n), coeficiente de absorción (α) y brecha de energía prohibida (Gap), además del espesor aproximado de la película; con el programa desarrollado se calcularon las constantes ópticas de películas delgadas de ZnS, SnS:Bi y SnS2:Bi, que son usadas como capas buffer y absorbentes en celdas solares, en este trabajo se presentan los resultados obtenidos con una película de SnS2:Bi. El software fue creado en el lenguaje de programación Python dentro de una interfaz sencilla inglés-español y para desarrollarlo se tuvo en cuenta el método propuesto por Swanepoel, el cual toma como base el espectro de transmitancia experimental del material semiconductor.

Control of slanting angle, porosity, and anisotropic optical constants of slanted columnar thin films via in situ nucleation layer tailoring

Electron-beam evaporation at a glancing angle of 85° is utilized to fabricate highly ordered, spatially coherent titanium slanted columnar thin films. Prior to deposition of the slanted columnar thin films, a titanium nucleation layer is deposited using electron-beam deposition at normal incidence with various intended nucleation layer thicknesses of 0nm, 5nm, 7.5nm, 10nm, 20nm, and 50nm. Structural and optical properties of the anisotropic porous thin films are studied by scanning electron microscopy, atomic force microscopy, and Mueller matrix generalized spectroscopic ellipsometry in the near infrared to ultra-violet spectral regions. An anisotropic effective medium approximation is employed for analysis of the ellipsometry data in order to determine slanting angle and porosity model parameters. We find that the slanting angle and titanium volume fraction are strongly influenced by the nucleation layer thickness. Structural parameters of SCTFs deposited on 50nm nucleation layers are similar to those from SCTFs with no nucleation layer. For small nucleation layer thicknesses, the corresponding SCTF slanting angle and titanium volume fraction decrease reaching a minimum of ≈33° and ≈12%, respectively, at 10nm nucleation layer thickness. In accordance with the strong decrease in volume fraction we observe substantial reduction of the effective anisotropic thin film optical constants. We find the slanting angle and porosity variation reproducible and suggest use of a nucleation layer for control of slanting angle and porosity of slanted columnar thin films.

Model-blind characterization of thin-film optical constants with momentum-resolved reflectometry.

Determining optical constants of thin material films is important for characterizing their electronic excitations and for the design of optoelectronic devices. Spectroscopic ellipsometry techniques have emerged as the predominant approach for measuring thin-film optical constants. However, ellipsometry methods suffer from complications associated with highly model-dependent, multi-parameter spectral fitting procedures. Here, we present a model-blind, momentum-resolved reflectometry technique that yields accurate and precise optical constants, with quantifiable error estimates, even for film thicknesses less than 50 nm. These capabilities are demonstrated by interrogating an optical absorption resonance in films of the polymer P(NDI2OD-T2). We show that this approach produces exceptional agreement with UV-Vis-NIR absorption measurements, while simultaneously avoiding the need to construct complicated multi-oscillator spectral models. Finally, we use this procedure to resolve subtle differences in the out-of-plane optical properties of different film morphologies that were previously obscured in ellipsometry measurements.

Characterization of thin-film thickness

Analysis methods and instrumentation for obtaining optical parameters and thickness profiles of thin-film samples from spectrophotometric and ellipsometric measurements are presented. Measured samples include thermally grown and evaporated SiO2 on a silicon substrate and a polymer photoresist layer on silicon. Experimental results at multiple sample positions give the thickness uniformity and optical constants of thin films. The thickness results obtained with spectrophotometry and ellipsometry agree within 1 nm for the 300 nm thick layer of SiO2 on silicon. For the 1600 nm thick resist sample the agreement of the measurement methods is within 8 nm. For the sample with a nominally 6000 nm thick layer of SiO2 on silicon, there is a deviation of ∼100 nm between the spectrophotometry and ellipsometry results. As an application, the optical parameters of a SiO2 layer on an induced junction silicon photodiode are determined by spectrophotometry and are used to confirm earlier values and uncertainties of the SiO2 refractive index and layer thickness non-uniformity.

Optical Constants of Thin Film Prepared by the Cd(OH)<SUB>2</SUB> Nanowires Synthesized Using the Arc Discharge Method

Optical Constants of Thin Film Prepared by the Cd(OH)<SUB>2</SUB> Nanowires Synthesized Using the Arc Discharge Method

Determination of the optical constants of thin films based on normal-incidence reflectance measurements

Complex-valued optical constants of thin films can be determined in various ways, such as polarization changes upon grazing reflection and simultaneous measurements of the reflectance (R) and the transmittance. In this work, we report that the reflectance-only measurement in normal incidence can also be used to evaluate optical constants when it is combined with two-step analysis methods, i.e., the Kramers-Kronig transformation of R to obtain the phase change upon the reflection and the numerical analysis of the Fresnel equation. By examining the influences of the uncertainty in R or in the phase on the final results, we show that the precise measurement of R over a broad spectral range is essential to guarantee the accuracy of the optical constants determined in this method.

ОптичнІ властивостІ ТіО2:Mn дО І післЯ термічноЇ обробкИ

The envelope method was employed to determine optical constants of thin films of TiO 2 and TiO 2 : Mn produced by electron-beam evaporation in a vacuum. The effect of thermal treatment on the optical properties of thin films was investigated