Forouhi Bloomer Model Research Articles

Optical investigation of Si:SiO2/SiO2 film

The optical properties of 30-layer [nc-Si:SiO2/ SiO2]30 periodic films have been studied. The films were prepared by alternately evaporating SiO and SiO2 onto Si(100) substrates, followed by annealing at 1100 ◦C. Spectroscopic ellipsometry spectrum analysis was used to deter- mine the optical constants of the samples via the Forouhi–Bloomer model. The optical bandgap of a single periodic film is calculated. The photoluminescence (PL) spectra of three samples with different thicknesses clearly show that there are two physical origins of the PL process.

Method for bandgap interpolation of perovskite's spectral complex refractive index.

Lead halide perovskites are a promising class of materials for solar cell applications. The perovskite bandgap depends on the material composition and is highly tunable. Opto-electrical device modelling is commonly used to find the optimum perovskite bandgap that maximizes device efficiency or energy yield, either in single junction or multi-junction configuration. The first step in this calculation is the optical modelling of the spectral absorptance. This requires as input the perovskite's complex refractive index N as a function of wavelength λ. The complex refractive index consists of real part n(λ) and imaginary part k(λ). For the most commonly used perovskites, n and k curves are available from spectroscopic ellipsometry measurements, but usually only for a few discrete bandgap energies. For solar cell optimization, these curves are required for a continuous range of bandgap energies. We introduce new methods for generating the n and k curves for an arbitrary bandgap, based on interpolating measured complex refractive index data. First, different dispersion models (Cody-Lorentz, Ullrich-Lorentz and Forouhi-Bloomer) are used to fit the measured data. Then, a linear regression is applied to the fit parameters with respect to the bandgap energy. From the interpolated parameters, the refractive index curve of perovskite with any desired bandgap energy is finally reconstructed. To validate our method, we compare our results with methods from literature and then use it to simulate the absorptance of a single junction perovskite and a perovskite/silicon tandem cell. This shows that our method based on the Forouhi-Bloomer model is more accurate than existing methods in predicting the complex refractive index of perovskite for arbitrary bandgaps.

Isotropic and Anisotropic Complex Refractive Index of PEDOT:PSS.

In this work, the complex refractive indexes of seven PEDOT:PSS samples, three with isotropic behavior and four with optical anisotropy, were determined. For the anisotropic samples, the ordinary and extraordinary components of the refractive index were described. The effect of the film thickness, measurement technique and preparation method on the extinction coefficient (k) and refractive index (n) of each sample was also discussed. Important differences (up to 20% in the average n) were found among the samples investigated. In most anisotropic films, the mean value of the extraordinary component was between 7 and 10% higher than that of the ordinary. In the three isotropic films, the average k rose when the film thickness increased. Moreover, the different sets of refractive index data were fitted to three different models: the original Forouhi-Bloomer model, the Liu (2007) model and the revised version of the Forouhi-Bloomer model (2019). In general, Liu's model gave better results, with small errors in n and k (<7.81 and 4.68%, respectively, in all the cases). However, this model had seven fitting parameters, which led to significantly longer computation time than the other two models. The influence of the differences in the measurement of the complex refractive index on the simulation of the optical properties of PEDOT:PSS multilayers was discussed. The results showed that n must be known precisely to accurately calculate the light absorption in a multilayer, without ignoring the isotropic or anisotropic behavior of the material or the influence of the layer thickness on its optical properties. This study aids in the development of simulation and optimization tools that allow understanding the optical properties of PEDOT:PSS films for their potential applications in organic optoelectronic devices, such as organic solar cells.

Precise spectrophotometric method for semitransparent metallic thin-film index determination using interference enhancement

A precise spectrophotometric method to determine the refractive index of a semitransparent metallic thin film is presented. This method relies on interference enhancement of the measured spectra, employing an opaque substrate with a dielectric spacer layer beneath the absorbing layer of interest to create interference fringes.The resulting spectral oscillations of the stack are highly sensitive to the properties of the top absorbing layer, allowing precise determination of the refractive index via fitting. The performance of this method is verified using simulations in comparison to the typical method of depositing the absorbing thin film directly onto a transparent substrate. An experimental demonstration is made for titanium thin films over the visible range (370-835 nm). The refractive index of these films is extracted from experimental data using a combination of the Modified Drude and Forouhi-Bloomer models. This method showed high repeatability and precision, and is verified for Ti films between 6-70 nm thickness.

PL study of Si:SiO2/SiO2 multilayer film

The optical properties of 30-layer [nc-Si:SiO2/ SiO2]30 periodic films have been studied. The films were prepared by alternately evaporating SiO and SiO2 onto Si(100) substrates, followed by annealing at 1100 ◦C. Spectroscopic ellipsometry spectrum analysis was used to deter- mine the optical constants of the samples via the Forouhi–Bloomer model. The optical bandgap of a single periodic film is calculated. The photoluminescence (PL) spectra of three samples with different thicknesses clearly show that there are two physical origins of the PL process.

Fabrication and characterization of graphene induced Metal Semiconductor Metal (MSM) structure for detection and sensing applications

The demand for miniaturization of electronic devices has lent to the development of graphene-based hybrid structures, which include the Metal-Semiconductor-Metal (MSM) device. In this work, one has developed such a device by growing monolayers of graphene on top of Nickel to form the basic structural matrix. Four different variants of the MSM unit structures have been developed to assess their potential in next generation electronics. The presence of graphene in the original matrix was confirmed via Atomic Force Microscopy, and the optical response of the graphene layer was further studied using Spectroscopic Ellipsometry in UV-Vis-NIR regime; Forouhi-Bloomer model was used to analyze the ellipsometry data. Hall effect and other electrical characterization measurements were conducted to analyze the electrical properties of the fabricated devices.

A comparison among the results of various dispersion relations for the ellipsometric data of Mn:ZnO thin films using PSO algorithm

Using particle swarm optimization (PSO) algorithm, the Cauchy, Forouhi-Bloomer (FB) and Sellmeier parametrization models were compared for the Mn doped ZnO (Mn:ZnO) thin films. The variation of both refractive and extinction coefficients with Mn concentration was also discussed. Our calculations demonstrate that despite the Sellmeier model exhibits the best fit with the lowest root-mean-square error (RMSE) in the transparent region, the FB model is well-suited in the both transparent and absorbing areas. Different energy gaps, roughnesses and thicknesses were obtained by the mentioned models. A comparison with the results of Tauck-Loretz model along with an exciton-based dielectric function were also done for our results.

Evaluation of the spectroscopic ellipsometry and dielectric properties of Cr2O3 nanoparticles doped PVDF thin films for future application of organic ferroelectric junctions

Here, we report the synthesis of Cr2O3 nanoparticles via ethylene glycol assisted microwave approach. Thin films of Cr2O3 nanoparticles doped Poly(vinylidene fluoride) (PVDF), at a variety concentrations (0.01–0.09wt%), were prepared by spin-coating technique on quartz substrate with thickness of 200nm. The influence of the concentrations of Cr2O3 nanoparticles on the structural, morphological, optical and dielectric properties of the PVDF is examined. The optical properties of the Cr2O3/PVDF thin films were examined by the ellipsometry and fitted by Forouhi–Bloomer model. The doping of PVDF by 0.05wt% of Cr2O3 nanoparticles showed an enhancement of the index of refraction compared to the neat PVDF. A remarkable enhancement of the dielectric constant was achieved when the PVDF film doped with 0.05wt% of Cr2O3 nanoparticles with 35 orders of magnitude compared to the neat PVDF film, owing to the Maxwell–Wagner–Sillars polarization effect. This results in an enhancement of the ferroelectric properties of the PVDF by increasing its remnant polarization from 8.7μC/cm2 to 12.1μC/cm2. These superior properties may enable the developed Cr2O3/PVDF films to be a potential candidate in the field of organic ferroelectric random access memory junctions.

Optical characteristics of wet-thermally oxidized bulk and nanoporous GaN

Gallium nitride (GaN) films deposited on sapphire substrates by metal organic chemical vapor deposition were successfully transformed into bulk and nanoporous gallium oxide (Ga2O3) using a wet thermal oxidation technique. Oxidation depth measurements confirmed that the oxide growth appeared to be faster in the case of nanoporous GaN than that of bulk GaN. Spectroscopic ellipsometry was used to evaluate and compare the optical properties of nanoporous and bulk Ga2O3 films, such as refractive index and extinction coefficient, which revealed improved optical properties for nanoporous Ga2O3 compared to the bulk. The simulations conducted on the ellipsometric spectra for bulk and nanoporous Ga2O3 using the Forouhi-Bloomer model and the Bruggeman effective medium approximation revealed the best fit with a low mean square error value. In the case of nanoporous Ga2O3, zero absorption was observed in the wavelength range of 300 nm to 840 nm, supporting the use of this material as a transparent coating in optoelectronic devices.

Structure and spectroscopic analysis of the graphene monolayer film directly grown on the quartz substrate via the HF-CVD technique

Direct growth of a monolayer graphene film on a quartz substrate by a hot filament chemical vapor deposition technique is reported. The monolayer graphene film prepared was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The optical properties were studied by spectroscopic elliposmetry. The experimental data were fitted by the Forouhi-Bloomer model to estimate the extinction coefficient and the refractive index of the monolayer graphene film. The refractive index spectrum in the visible region was studied based on the harmonic oscillator model. The lattice dielectric constant, real and imaginary dielectric constants and the ratio of the charge carrier number to the effective mass were determined. The surface and volume energy loss parameters were also found and showed that the value of the surface energy loss is greater than the volume energy loss. The determination of these optical constants will open new avenue for novel applications of graphene films in the field of wave plates, light modulators, ultrahigh-frequency signal processing and LCDs.

Substrate temperature dependence of structural, morphological and optical properties of Sn4Sb6S13 thin films deposited by vacuum thermal evaporation

In this work, structural and morphological properties of Sn4Sb6S13 thin films grown by single source thermal evaporation were investigated. The films were deposited onto glass substrates heated in the temperature range 30–200°C then characterized by XRD, AFM, SEM and Raman spectroscopy. The films are preferentially oriented along the (6¯11) plane. Analysis of the surface morphology reveals that the films had an average roughness increasing from 2.81 to 8.23nm as the substrate temperature increases from 30 to 200°C. The variations of the microstructural parameters, such as crystallite size (D), dislocation density (δ), the number of crystallites per unit area (N), the stacking fault probability (P) and strain (ε) with substrate temperature were investigated. Raman measurement was used to obtain more information about structural changes of Sn4Sb6S13 films. The optical parameters were deduced by using Forouhi-Bloomer models.

The optical dielectric model of Cu2O thin film and its verification

The transmittance and reflectance of cuprous oxide (Cu2O) thin film deposited on quartz substrate were measured by a spectrophotometer. Use the optical dielectric model combining the Forouhi–Bloomer model with modified Drude model (FBM+MDM), the optical constants, as well as the thickness of Cu2O film were attained from its measured transmittance data. Moreover, by means of the TFCalc software, the reflectance and transmittance were calculated conversely from the optical constants (n, k) and the thickness of the Cu2O film. It was found that the calculated reflectance and transmittance were in good agreement with the measured ones. So the optical dielectric model, namely FBM+MDM, is suitable for Cu2O thin film.

Correlation between microstructural and optical properties of silicon thin films grown onto porous alumina by plasma–enhanced CVD method

The silicon nanocrystals (Si NCs) are fabricated on a porous alumina (PAl) matrix by PECVD technique at different deposition time (dt) in order to produce PAlSi thin films with a high crystallinity. In this work, we report a correlation between microstructural and optical characterizations of PAlSi alloy in term of volumic Si NCs fraction and mainly the Si NCs sizes. The morphology and structure of the samples were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X–ray spectroscopy (EDX), X–Ray Diffraction (XRD) technique, and Raman spectroscopy. Optical properties of the microstructure were studied using spectroscopic ellipsometry (SE) data. Based on the SE data, an appropriate optical model is used to describe the PAlSi content with various volumic fraction of Si NCs. Bruggeman effective medium approximation and Forouhi-Bloomer models are used to analyze the effects of the volumic crystalline Si fraction on the optical properties of PAlSi, such as the refractive index (n), extinction coefficient (k) and energy band gap (Eg), as well as the dielectric functions. We show that the crystallization process is strongly dependent on the degree or the volumetric fractions of Si NCs embedded in a PAl matrix.

OPTICAL PROPERTIES OF N-DOPED Cu2O THIN FILMS DEPOSITED BY RF-MAGNETRON SPUTTERING Cu2O TARGET

N -doped Cu 2 O films were deposited on quartz substrates by reactive magnetron sputtering a Cu 2 O target. The optical constants and thicknesses of the films with different nitrogen partial pressure (NPP) were retrieved from transmittance data by an optical model which combines the Forouhi–Bloomer model with modified Drude model. The results show that when NPP increases from 0.0 to 0.033 Pa, the optical gap decreases from 2.14 to 1.95 eV. Additionally, an optical absorption process in the infrared region below the optical band gap was observed for N -doped Cu 2 O films, which was not found in the pure Cu 2 O film. This is because an intermediate band (IB) in the band gap results from nitrogen doping. It is believed that N -doped Cu 2 O film with suitable NPP could be used to enhance the energy conversion efficiency for photovoltaic cells.

Thickness effect on the structural and optical constants of stibnite thin films prepared by sulfidation annealing of antimony films

This paper deals with some physical properties of antimony sulphide Sb2S3 thin films obtained by an annealing process in sulphur vapors at 300°C of Sb thermal evaporated thin films deposited on glass substrate. The crystal structure and surface morphology were investigated by both XRD and AFM techniques. This structural study shows that Sb2S3 thin films were well crystallized in orthorhombic structure and some parameters such as the lattice parameter, crystallite size, microstrain and degree of preferred orientation have been reported and correlated with the effect of crystallite size. On the other hand, the refractive index and the extinction coefficient were discussed in terms of the Forouhi–Bloomer model. The optical band gap was found to range from 1.75 to 2.23eV. Finally, the analysis of the optical parameters extracted from the Urbach–Martienssen and Forouhi–Bloomer models lead to some explanations of the correlations between the structural properties in terms of the crystallite size and optical ones.

Optical and photocatalytic properties of composite TiO2/ZnO thin films

Pure TiO2 and ZnO thin films named Ti100 and Zn100 were prepared via sol–gel technique using Ti alkoxide and Zn acetate as metal precursors and dip coating deposition on quartz substrate. Different vol.% ratios of the initial Ti and Zn solutions were used to obtain composite TiO2/ZnO films nominated as Ti25, Ti50 and Ti75. The XRD patterns of pure TiO2 and ZnO films revealed the formation of anatase TiO2 and wurtzite hexagonal ZnO, respectively. The patterns of the composite film Ti75 were similar to the pure TiO2, while the composite films Ti25 and Ti50 revealed amorphous structure. The XPS analysis proved presence of TiO2 and ZnO oxide phases in the pure and composite films that is in accordance with XRD analysis. The UV–vis transmission spectra of the films showed that absorption edges of the composite films were blue shifted in comparison with the pure films. The largest shift was attained in the Ti25 composite film. The Forouhi–Bloomer (FB) and Tauc–Lorentz (TL) dispersion models were used for description of the complex refractive index of the films and for estimation of their thickness and energy band gap. The refractive index in the films’ transparency region and high energy region increased with the increase of TiO2 phase content. The thickness of the films also increased with the increase of TiO2 content. The pure TiO2 film was approximately 2.5 times thicker (145nm) than the pure ZnO film (60nm). The estimation of the energy gaps showed comparable gap value of ∼3.2eV for the pure oxide films. The largest value of ∼3.8eV was calculated for the Ti25 composite film. A good agreement between the two models was observed in the estimation of gap and thickness values. For pure ZnO film, better accordance between experimental and theoretical transmittance spectra was achieved via FB model simulations in the region above the band gap. The photocatalytic properties of the films in air purification were investigated via standard NO oxidation procedure. The Ti100 and Ti75 films exhibited improved performance in comparison to Ti25 and Zn100 films. The highest photocatalytic efficiency of 1.6×10−2mol/einstein in NO oxidation was recorded for pure TiO2 film. Also, the latter showed the highest hydrophylicity without and under UV illumination.

Dispersion model for optical constants of a-Si:H

The optical constants of hydrogenated amorphous silicon (a-Si:H) deposited by plasma enhanced chemical vapor deposition (PECVD) have been obtained using the Forouhi–Bloomer (FB) model and the Tauc–Lorentz (TL) model, respectively. It is indicated that there are some discrepancies between the results derived from the FB model and the TL model. Based on the theory background of the two models, a detailed analysis on these discrepancies has been carried out. Finally, we have proposed a modified FB model to reduce the physical imperfection of the original FB model. This model can better fit the optical constants of a wide variety of amorphous silicon with different microstructures.

Optical properties investigation of [nc-Si:SiO2/SiO2]30 periodic multilayer films

The optical properties of 30-layer [nc-Si:SiO2/SiO2]30 periodic films have been studied. The films were prepared by alternately evaporating SiO and SiO2 onto Si(100) substrates, followed by annealing at 1100 ∘C. Spectroscopic ellipsometry spectrum analysis was used to determine the optical constants of the samples via the Forouhi–Bloomer model. The optical bandgap of a single periodic film is calculated. The photoluminescence (PL) spectra of three samples with different thicknesses clearly show that there are two physical origins of the PL process.

Parametrization of the Forouhi–Bloomer–Lorentz model for Ta_2O_5 films in the fundamental-absorption region

The complex optical and dielectric functions of the energy of an electromagnetic wave are calculated for a film of tantalum (V) oxide in the short-wavelength region, including the fundamental-absorption region. An additive combination of the Forouhi–Bloomer and Lorentz models is constructed to compute these functions. Versions of the Forouhi–Bloomer model with a dipole-transition matrix element that is independent of the wave energy are considered, along with a modified model. It is established that the modified model has an advantage when describing broad-band dielectric amorphous media. The optical band gap computed from the Forouhi–Bloomer and Lorentz models is compared with the value determined from the Tautz extrapolation.

Comparison of different dispersion models for single layer optical thin film index determination

Abstract We here determine the optical properties of different single-layer thin films containing Ta 2 O 5 , Si, Indium Tin Oxide and Au in the ultraviolet–visible and near infrared ranges. More specifically, we deduce the complex refractive index and thickness from the reflectance and transmittance measured using a spectrophotometer at normal incidence. One major difficulty is to find an appropriate selection of dispersion laws for various types of material (dielectric, semiconductors, and metals). For this purpose, a number of models have been investigated from a theoretical point of view in consideration of the Kramers–Kronig relation. These include the Forouhi–Bloomer model, combined with the modified Drude, Tauc–Lorentz and multiple-oscillator Tauc–Lorentz models. A global optimization procedure had to be employed because of the large number of parameters (from 3 to 15) required to describe the optical dispersion laws. The calculated reflectance and transmittance are in good agreement with experimental data and the complex refractive index is consistent with our knowledge and that already reported.