Swanepoel Envelope Method Research Articles

The Impact of Temperature and Power Variation on the Optical, Wettability, and Anti-Icing Characteristics of AZO Coatings

The structural, wettability, and optical characteristics of aluminum-doped zinc oxide (AZO) thin films were studied with the objective of understanding the impact of deposition power and deposition temperature. Thin films were deposited using a radio frequency (RF) magnetron sputtering technique. The power output of the RF was augmented from 200 to 260 W, and the temperature was increased from 50 to 200 °C, which led to the development of a (002) peak for zinc oxide. The study of film thickness was carried out using the Swanepoel envelope method from data obtained through the UV-Vis spectrum. An increase in surface roughness value was shown to be connected with fluctuations in temperature as well as increases in deposition power. The findings revealed that as deposition power and temperature increased, the value of optical transmittance decreased, ranging from 70% to 90% based on the deposition parameters within the range of wavelengths that extend from 300 to 800 nm. The wettability properties of the samples were studied, and the maximum contact angle achieved was 110°. A Peltier apparatus was utilised in order to investigate the anti-icing capabilities, which revealed that the icing process was slowed down 3.38-fold. This work extends the understanding of the hydrophobicity and anti-icing capabilities of AZO thin films, specifically increasing both attributes which provide feasible options for purposes requiring resistance to ice.

Retrieval of Optical Constants of Undoped Flash-Evaporated Lead Iodide Films from an Analysis of Their Normal Incidence Transmission Spectra Using Swanepoel’s Transmission Envelope Theory of Non-Uniform Films

Abstract: Normal-incidence transmission-wavelength (T_exp (λ)-λ) spectra of 1 and 1.2 m thick flash-evaporated lead iodide (PbI2) films on 1.1 mm thick glass slides held at 200 ℃ display well-spaced several interference-fringe maxima and minima in the λ-range 520-900 nm, without exhibiting a transparent region and with the maxima lying well below the substrate transmission. Below 520 nm, these T_exp (λ)-λ curves drop steeply to zero (at λ ≼ 505 nm), signifying crystalline-like PbI2 film absorption. As corrections of measured (PbI2 film/substrate) transmittance data for substrate absorption and spectrometer slit-width effect were marginal over the studied λ-range, the observed low transmittance of (PbI2 film/substrate) system was related to PbI2 film thickness non-uniformity (∆d), which causes shrinkage of both maxima and minima and leads to significant film optical absorption that reduces both maxima and minima. The McClain ENVELOPE algorithm was utilized, with a minor modification, to construct maxima T_M (λ_max/λ_min) and minima T_m (λ_min/λ_max) envelope curves, which were analyzed by Swanepoel’s envelope method of non-uniform films using an approach that takes account of dispersive substrate refractive index n_s (λ) and circumvents the non-availability of a high-λ transparency region. In such analytical approach, ∆d was varied till a re-generated T_gen (λ)-λ curve matches the T_exp (λ)-λ curve. An average thickness d ̅ of the film, besides its refractive index n(λ) and absorption coefficient α(λ) in the weak, medium and strong absorption regions, were then obtained. The energy-dependence of α(λ) is discussed in view of interband electronic transition models. The obtained results are consistent with other literature studies on similar flash-evaporated PbI2 films. Keywords: PbI2, Optical constants and bandgap, Swanepoel's transmission envelope method, Non-uniform films.

Dereceli ve derecesiz InGaN/GaN MQW’lerin dielektrik özellikleri

In this study, dielectric properties of graded and non-graded InGaN/GaN multi quantum wells (MQWs), grown on sapphire(Al2O3) wafer by Metal Organic Chemical Vapor Deposition (MOCVD) technique, are investigated. In order to notice graded layer effect on characteristics of MQWs some of GaN layers are grown by doping In atoms. Dielectric function of films are determined by Swanepoel envelope method. Real and imaginer dielectric coefficient of the films are calculated by using refraction index and extinction coefficient. Differences in refraction index values are discussed for graded and non-graded samples. During determination of dielectric function variations of complex and imaginer dielectric coefficients with photon energy are shown for both samples

Investigation of amorphous-crystalline transformation induced optical and electronic properties change in annealed As50Se50 thin films

The present work reports the amorphous-crystalline phase transformation in thermally evaporated As50Se50 thin films upon annealing at below Tg (423 K) and above Tg (523 K). The structural transition was probed by XRD, Raman and X-ray photoelectron spectroscopy. The composition and surface morphology were probed by EDS and FESEM techniques. The transmittance and reflectance spectra over the wavelength range 500 nm–1200 nm were used to deduce the optical parameters. The various optical parameters of the as-prepared and annealed As50Se50 thin films were estimated and discussed in terms of density of defect states and disorders. The indirect optical energy gap decreased for the 423 K annealed film and abruptly increased for 523 K annealed film as compared to the as-prepared film. The Swanepoel envelope method, WDD model, and Sellemeire postulates were employed for the analysis of refractive index, static refractive index, oscillator energy, dispersion energy, oscillator wavelength and dielectric constant. The changes in the linear and nonlinear properties showed opposite behavior for the two annealed films. The non-linear refractive index and 3rd order susceptibility were found to be increased for 423 K annealed film and decreased for the 523 K annealed film. The optical as well as the electrical conductivity changed with annealing and the electrical susceptibility increased for 523 K annealed film. The tunable optical properties can be applied for several optoelectronic applications. The amorphous to crystalline structural transformation occurred at annealing above Tg. The 3rd order susceptibility was found to be more at 423 K annealing and less at 523 K annealing.

Linear and nonlinear optical studies of thermally evaporated chalcogenide a-Pb-Se-Ge thin films

This article is dedicated to studying optical characteristics of thermally evaporated Pb10Se90-xGex (0.0 ≤ x ≤ 10.0 at.%) thin films. These films were deposited on pre-cleaned high-quality glass substrates under a vacuum about 5 × 10−4 Pa. The amorphous nature of films was affirmed by X-ray diffractograms. Elemental analysis was done by Energy-dispersive X-ray spectroscopy. Optical properties of Pb–Se-Ge films were studied and investigated using the transmission spectra. Thickness of the films and refractive index were computed utilizing Swanepoel envelope method. Wemple-Di-Domenico model was applied to get dispersion energies and oscillator parameters. Absorption coefficient values of films were estimated and found to be of the order of 10−4cm−1. The electronic transitions of a-Pb10Se90-xGex thin films were resulted from allowed indirect transitions and the optical band gap was found to decrease from 1.623 eV to 1.538 eV with increasing Ge-ratio while Urbach energy was found to increase from 61 meV to 86 meV. All discussed parameters strongly depend on the Ge-concentration.

Optical and structural modification in amorphous Ge24Se61Sb15 thin films under 80 MeV Silicon swift heavy ions for telecom and optical applications

Present study reports about the effect of 80 MeV Silicon swift heavy ions irradiation on linear and nonlinear optical properties of amorphous Ge24Se61Sb15 thin films. Optical changes are correlated with structural modifications for their utilization in telecom and optical applications. Optical transmission spectra were recorded from 200 nm to 1100 nm. Linear refractive index is calculated by optical transmission using Swanepoel envelope method. Dispersion in the linear refractive index of the thin films is described using Wemple-DiDomenico model. Nonlinear optical parameters are determined using semi-empirical relations. Optical band gap is calculated by extrapolating the Tauc's plot. The investigation shows that optical band gap decreases from 1.64 eV to 1.47 eV and linear refractive index increases from 2.50 to 2.59 till fluence 1 × 1012 ions/cm2. In addition, third-order nonlinear susceptibility increases from 8.178 × 10−10 [esu] to 11.43 × 10−10 [esu] and nonlinear refractive index increases from 1.742 × 10−10 [esu] to 2.698 × 10−10 [esu] till fluence 1 × 1012 ions/cm2. Raman measurements reveal that swift heavy ion irradiation converts homopolar Ge–Ge, Sb–Sb bonds into hetropolar Ge–Sb and Se–Sb bonds, which is responsible for observed optical changes. The changes are understood in terms of glass network structure and electronic energy loss for application point of view.

Switching of linear and nonlinear optical parameters in As35Se65 thin films upon annealing at both above and below Tg

The present manuscript investigated the effect of thermal annealing at 150 °C (below Tg) and 250 °C (above Tg) on the nonlinear as well as linear optical parameters and structural changes of the thermally evaporated As35Se65 thin films. The structural investigation was done by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, whereas the surface morphology was studied by field emission scanning electron microscopy. The optical transmission and reflection spectra over the wavelength range 500–1200 nm were used to calculate the optical parameters. The optical energy gap, Urbach energy, optical density, skin depth, Tauc parameters for the as-deposited and annealed As35Se65 films were estimated and discussed in terms of density of defect states and disorders. The indirect optical energy gap decreased for 150 °C annealed film and abruptly increased for 250 °C annealed film as compared with the as-prepared film. The Swanepoel envelope method, WDD model, and Sellemeire postulates were employed for analysis of refractive index, static refractive index, dispersion energy, oscillator wavelength, oscillator energy, and dielectric constant. The non-linear refractive index and third-order susceptibility were also estimated with the help of empirical relations which showed opposite changes for the two annealing temperatures. The tunable optical properties can be applied for several optoelectronic application.

Optical and structure properties of CdTe/CdS films under influence of both CdCl2 heat treatment and (O2 + Ar) atmosphere

Thin films of CdTe/CdS were prepared using the thermal evaporation technique with pressure 2 × 10−5 mbar on substrate from glass. The thickness of CdCl2 layer around 150 nm was deposited making as-deposited CdTe/CdS films. The films covered by cadmium chloride (CdCl2) layer were annealed in atmosphere of (O2 + Ar) at different temperatures of 400 °C, 450 °C and 480 °C for 15 min. The effect of CdCl2 as a top layer on morphological, structural and optical properties was studied, and the results were compared with as-deposited films and also with (O2 + Ar) annealing process. The refractive index in whole wavelength and film thickness was estimated by Cauchy dispersion relation and Swanepoel's envelope method, respectively. Furthermore, many optical parameters such as transmittance, absorbance, reflectance, and optical band gap, Urbach energy, film thickness, electronic polarizability, lattice dielectric constant were calculated also in this study. The heat treatment of our films with depositing CdCl2 layer in (O2 + Ar) flow lowered the energy gap which led CdTe/CdS films to be a candidate to work in thin-film solar cells as an absorber layer.

Swanepoel method for AlInN/AlN HEMTs

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV–Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV–Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.

Optical constants of rare-earth substituted amorphous oxide-mix-based layers deposited to enable synthesis of magneto-optic garnets

Amorphous oxide mixes used to synthesise ferrite-type rare-earth (RE) substituted garnets and garnet-oxide nanocomposite layers are prepared on clear glass substrates by using RF magnetron sputter-deposition process. By using a combination approach employing custom-built spectrum-fitting software in conjunction with Swanepoel's envelope method, the spectral dispersion function of optical constants and the layer thicknesses are derived accurately from the transmission spectra of the as-deposited samples. The effects of excess metal-oxides added to the base material systems during the co-deposition process are found to affect the refractive index and the optical absorption coefficients of garnet-oxide composites. A number of optical constant datasets are presented, enabling the experimentalists to design nanophotonic or integrated-optics devices employing these functional materials. The garnet compositions characterized (deposited by RF sputtering) have only been reported in annealed garnet layers till present, however, the optical constants of as-deposited films are also of interest for the design of magnetic multilayers.

Thickness-dependent microwave dielectric and nonlinear optical properties of Bi0.5Na0.5TiO3 thin films

Abstract Lead-free Bi0.5Na0.5TiO3 (BNT) films were grown on Pt(111)/Ti/SiO2/Si and quartz substrates for various thickness by using pulsed laser deposition technique. The impact of thickness on structural, microstructural, Raman-spectroscopy, microwave dielectric and nonlinear optical properties have been investigated in detail. X-ray diffraction pattern of BNT films deposited at 700 °C showed rhombohedral crystal symmetry with a small secondary phase of Bi4Ti3O12 and also revealed that the lattice parameters, lattice volume, strain and crystallite size were enhanced with film thickness. The film thickness, refractive index and optical bandgap have been determined by Swanepoel's envelope method and Tauc relation and are in the range of 208 nm–1300 nm, 3.79 eV–3.28 eV and 2.41–1.80, respectively. The third order nonlinear optical properties of films were estimated by Z-scan technique and the 208 nm film exhibited strong nonlinear refractive index (n2 = 4.62 × 10−6 cm2/W) and nonlinear absorption coefficient (β = 0.796 cm/W). The enhancement in microwave dielectric properties was observed with film thicknesses which were measured by using SPDR technique. The leakage current density exhibited the space charge limited current conduction behavior. The enhanced microwave dielectric and nonlinear optical properties of BNT films are promising for microwave tunable and nonlinear photonic device applications.

A detailed study on optical properties of InGaN/GaN/Al2O3 multi quantum wells

In this study optical properties of InGaN/GaN/Al2O3 multi-quantum well (MQW) structures are investigated in detail. Three samples containing InGaN/GaN/Al2O3 MQWs are grown by using metal organic chemical vapor deposition technique. Sapphire (6H–Al2O3) is used as the substrate. Forbidden energy band gaps (Eg) of these three samples are determined from photoluminescence and absorption spectra. Results gained from these two spectra are compared with each other. It is found that Eg values are between 2 and 3 eV. For determining refraction index, absorption coefficients, extinction coefficients and thickness of the films a rare method called Swanepoel envelope method is used. It is seen that results gained from this method are consistent with those in literature.

Optical band gap and dispersion of optical constants of Cu-Ga-S thin films

Thermally deposited Cu-Ga-S thin films were optically characterized by means of experimental techniques of transmission measurements. The analyses of transmittance spectra were accomplished by derivative spectrophotometry analyses to get gap energies of thin films. The transmittance spectra of thin films annealed at different temperatures presented interference fringes which were analyzed by Swanepoel envelope method. The wavelength dependencies of optical parameters; refractive index (n), real part of complex dielectric function (εre) and extinction coefficient (k) were reported in the weak absorption region. The photon energy dependencies of n and εre were analyzed using single-oscillator and Spitzer-Fan models, respectively.

Investigation on annealing temperature-dependent optical properties of electron beam evaporated ZnSe thin films

This research work is devoted to studying optical properties of zinc selenide (ZnSe) thin films deposited by electron beam evaporation technique and annealed at different temperatures in a nitrogen environment. The structural analysis by X-ray diffraction confirmed that the obtained ZnSe films had cubic zinc-blende structure with preferred orientation along plane (111). Based on Swanepoel's envelope method, some important optical parameters such as absorption coefficient, extinction coefficient, refractive index and optical band gap, were evaluated through the transmission spectrum ranging from 300 to 1500 nm at room temperature. The optical band gap increased from 2.52 to 2.65 eV with the increasing annealing temperature. However, both the thickness and refractive index of the films decreased. In addition, the dispersion parameters of the refractive index and energy were also studied by using Wemple-DiDomenico single oscillator model.

Effect of CdCl2 heat treatment in (Ar + O2) atmosphere on structural and optical properties of CdTe thin films

Cadmium telluride (CdTe) thin films were deposited by thermal evaporation method under base pressure 2 × 10−5 mbar on corning glass substrate. In this work, we study the effect of cadmium chloride (CdCl2) heat treatment in argon and oxygen (Ar + O2) atmosphere on the structural, morphological and optical properties of CdTe thin films to achieve high quality thin film absorber layer for solar cells applications. The structural characteristics were studied by X-ray diffraction (XRD). The microstructure parameters of the films such as average grain size (Davg), average lattice strain (εavg) and dislocation density (ρD) have been calculated via XRD line broadening analysis. XRD investigation revealed that, the samples show polycrystalline nature pronounced with cubic zinc blende structure with a strong preferentially (1 1 1) texture orientation. It has been found that the crystallinity of the films enhanced during (Ar + O2) annealing and CdCl2 heat treatment. The surface morphology of CdTe thin films was investigated by field emission scanning electron microscope (FE-SEM). XRD and FE-SEM results of CdCl2 treated films showed recrystallization and progressive increase in grain size. The optical properties of all samples were estimated using UV–vis–near-infrared (NIR) spectrophotometer. The Swanepoel envelope method has been employed to evaluate the various optical parameters of CdTe films such as refractive index and film thickness. The as-deposited films have a relatively high value of refractive index of 2.54, in contrast the CdCl2 treated films have a relatively low value of 2.1 in the whole wavelength range. The optical energy gap values slightly decrease from 1.56 eV for as-deposited films up to 1.54 eV for CdCl2 heat treated films. CdCl2 heat treatment in (Ar + O2) atmosphere is found to be a promising method to improve the physical properties of CdTe thin film solar cells.

Effect of solution molarity on optical dispersion energy parameters and electrochromic performance of Co3O4 films

Co3O4 films were deposited on glass and FTO (F:SnO2) substrates by different solution molarities (0.05–0.20 M) through nebulizer spray technique. The crystalline quality of the films was evaluated by X-ray diffraction. The morphological variation of Co3O4 films for different solution concentration was observed from scanning electron microscopy. Optical constants (n and k) and dispersion energy parameters were calculated by fitting the transmittance curves using Swanepoel envelope method. The electrical parameters such as sheet resistance and activation energy were estimated using four probe method. The electrochromic performance of the films was analyzed by electrochemical measurements such as cyclic voltammetry, chronoamperometry, chronocoulometry and optical contrast studies.

Effect of antimony (Sb) addition on the linear and non-linear optical properties of amorphous Ge–Te–Sb thin films

Non-crystalline thin films of Ge20Te80−xSbx (x = 0, 2, 4, 6, 10) systems were deposited on glass substrate using thermal evaporation technique. The optical coefficients were accurately determined by transmission spectra using Swanepoel envelope method in the spectral region of 400–1600 nm. The refractive index was found to increase from 2.38 to 2.62 with the corresponding increase in Sb content over the entire spectral range. The dispersion of refractive index was discussed in terms of the single oscillator Wemple–DiDomenico model. Tauc relation for the allowed indirect transition showed decrease in optical band gap. To explore non-linearity, the spectral dependence of third order susceptibility of a-Ge–Te–Sb thin films was evaluated from change of index of refraction using Miller’s rule. Susceptibility values were found to enhance rapidly from 10−13 to 10−12 (esu), with the red shift in the absorption edge. Non-linear refractive index was calculated by Fourier and Snitzer formula. The values were of the order of 10−12 esu. At telecommunication wavelength, these non-linear refractive index values showed three orders higher than that of silica glass. Dielectric constant and optical conductivity were also reported. The prepared Sb doped thin films on glass substrate with observed improved functional properties have a noble prospect in the application of nonlinear optical devices and might be used for a high speed communication fiber. Non-linear parameters showed good agreement with the values given in the literature.

Optical investigation of vacuum evaporated Se80−xTe20Sbx (x = 0, 6, 12) amorphous thin films

Amorphous thin films of Se80−xTe20Sbx (x=0, 6, 12) chalcogenide glasses has been deposited onto pre-cleaned glass substrate using thermal evaporation technique under a vacuum of 10−5Torr. The absorption and transmission spectra of these thin films have been recorded using UV spectrophotometer in the spectral range 400–2500nm at room temperature. Swanepoel envelope method has been employed to obtain film thickness and optical constants such as refractive index, extinction coefficient and dielectric constant. The optical band gap of the samples has been calculated using Tauc relation. The study reveals that optical band gap decreases on increase in Sb content. This is due to decrease in average single bond energy calculated using chemical bond approach. The values of urbach energy has also been computed to support the above observation. Variation of refractive index has also been studies in terms of wavelength and energy using WDD model and values of single oscillator energy and dispersion energy has been obtained.

Determination of the optical constants of As–Se–Ag chalcogenide thick films with high precision for optoelectronics applications

Thin films of (As50Se50)100−xAgx (with 0 ≤ x ≤ 25 s) metal-chalcogenide glasses were deposited onto glass substrates by thermal evaporation technique under high vacuum (10−6 mbar). The optical constants as well as the average thickness of the studied films are determined by the Swanepoel envelope method which is based on the optical transmission spectra measured in the spectral range 300–2500 nm. This method enables the transformation of the optical-transmission spectrum of a thin film of wedge-shaped thickness into the spectrum of a uniform film, whose thickness is equal to the average thickness of the non-uniform layer. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-oscillator model. The optical absorption edge is described using the non-direct transition model proposed by Tauc relation. Analysis of the optical data revealed that an addition of Ag in the range from 0 to 25 at.% to the (As50Se50)100−x binary alloys affected the optical parameters of the investigated thin films. For instance, the optical band gap decreased from 1.661 to 1.441 eV with increasing the Ag content from 0 to 25 at.%. The results were discussed in terms of Mott and Davis model as well as chemical-bond approach.

Synthesis and characterization of zinc oxide thin films for optoelectronic applications.

Micro-ring structured zinc oxide (ZnO) thin films were prepared on glass substrates by spray pyrolysis and their structural, morphological, optical and electrical properties were investigated. X-ray Diffraction (XRD) analysis revealed the films’ hexagonal wurtzite phase with a preferred (002) grain orientation. The mean crystallite size calculated on the basis of the Debye-Scherrer model was 24 nm and a small dislocation density of was obtained, indicating the existence of few lattice defects and good crystallinity. Scanning Electron Microscopy (SEM) micrographs revealed the film’s granular nature composed of rod-shaped and spherical nanoparticles which agglomerated to form micro-ring like film clusters on the film surface. The average transmittance in the visible region, optical band gap and Urbach energy were approximately 75–80%, 3.28 eV and 57 meV, respectively. The refractive index and extinction coefficient were determined using Swanepoel’s envelope method. Raman spectroscopy revealed the presence of small amounts of residual tensile stress and low density of defects in the ZnO thin films. This was consistent with XRD analysis. A low sheet resistivity and high figure of merit were obtained for our films indicating their suitability in optoelectronic applications.