Microstructural parameters and optical constants of ZnTe thin films with various thicknesses

Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed that the films are polycrystalline and have a zinc blende (cubic) structure. The calculated microstructure parameters revealed that the crystallite size increases and microstrain decreases with increasing film thickness. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 400-2500 nm. For ZnTe films of different thicknesses, the dependence of absorption coefficient, α on the photon energy showed the occurrence of a direct transition with band gap energy (For ZnTe films of different thicknesses) confirming the independency of deduced energy gap on film thickness. The refractive indices have been evaluated in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index could be extrapolated by Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. It was observed that the refractive index, n increased upon increasing the film thickness up to 508 nm, lying within the experimental error for further increases in film thickness.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Thickness dependent optical dispersion parameters and nonlinear optical properties of nanostructured Cr doped CdO thin films

Cr doped CdO thin films were deposited on glass substrates by reactive DC magnetron sputtering with varying film thickness from 250 to 400 nm. XRD studies reveal that the films exhibit cubic structure with preferred orientation along the (2 0 0) plane. The optical transmittance of the films decreases from 92 to 72%, whereas the optical energy band gap of the films decreased from 2.88 to 2.78 eV with increasing film thickness. The Wemple–DiDomenico single oscillator model has been used to evaluate the optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o), static refractive index (n_o) and high frequency dielectric constant (ε_∞). The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) of the films were also determined.     

Formation of Ge35In8S57 amorphous films for optical applications

Thin films of In-doped Ge-S in the form of Ge₃₅In₈S₅₇ with different film thickness were deposited using an evaporation method. The X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature for these films. Some optical constants were calculated at a thickness of 150, 300, 450 and 900?nm and annealing temperature of 373, 413, 437 and 513?K. Our optical observations show that the mechanism of the optical transition obeys the indirect transition. It was found that the energy gap, E_g, decreases from 2.44 to 2.20?eV with expanding the thickness of the film from 150 to 900?nm. On the other hand, it was found that E_g increases with annealing temperature from 373 to 513?K. The increment in the band gap can be attributed to the gradual annealing out of the unsaturated bonds delivering a decreasing the density of localized states in the band structure. Using the single oscillator model, the dispersion of the refractive index is described. The dispersion constants of these films were calculated with different both thickness and annealing temperatures. Additionally, both of nonlinear susceptibility, χ⁽³⁾ and nonlinear refractive index, n₂ were calculated.     

Effect of 60Co γ-irradiation on structural and optical properties of thin films of Ga10Se80Hg10

Thin films of Ga₁₀Se₈₀Hg₁₀ have been deposited onto a chemically cleaned Al₂O₃ substrates by thermal evaporation technique under vacuum. The investigated thin films are irradiated by ⁶⁰Co γ-rays in the dose range of 50–150 kGy. X-ray diffraction patterns of the investigated thin films confirm the preferred crystallite growth occurs in the tetragonal phase structure. It also shows, the average crystallite size increases after γ-exposure, which indicates the crystallinity of the material increases after γ-irradiation. These results were further supported by surface morphological analysis carried out by scanning electron microscope and atomic force microscope which also shows the crystallinity of the material increases with increasing the γ-irradiation dose. The optical transmission spectra of the thin films at normal incidence were investigated in the spectral range from 190 to 1100 nm. Using the transmission spectra, the optical constants like refractive index (n) and extinction coefficient (k) were calculated based on Swanepoel’s method. The optical band gap (E_g) was also estimated using Tauc’s extrapolation procedure. The optical analysis shows: the value of optical band gap of investigated thin films decreases and the corresponding absorption coefficient increases continuously with increasing dose of γ-irradiation.     

Optical band gap and refractive index dispersion parameters of As x Se70Te30−x (0≤x≤30 at.%) amorphous films

Amorphous As _x Se₇₀Te_30?x thin films with (0≤x≤30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T(λ) of the films at normal incidence were measured in the wavelength range 400–2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the As _x Se₇₀Te_30?x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content.     

Influence of thickness and annealing on linear and nonlinear optical properties of manganese (III) chloride tetraphenyl porphine (MnTPPCl) organic thin films

Thin films of manganese (III) chloride 5,10,15,20-tetraphenyl-21H,23H-porphine (MnTPPCl) with different film thickness were deposited by an evaporation technique. Some optical constants were calculated for these films at a thickness of 110, 220 and 330 nm and annealing temperature of 373 and 437 K. IR spectrum demonstrating that the thermal evaporation method is a good one to acquire undissociated and stoichiometric MnTPPCl films. Our perceptions demonstrate that the mechanism of the optical absorption obeys with the indirect transition. It was found that the energy gap, E_g, affected by the film thickness and annealing. Dispersion of the refractive index is described using single oscillator model. Dispersion parameters are calculated as a function of the film thickness and annealing temperature. In addition, the third-order nonlinear susceptibility, χ⁽³⁾, and the nonlinear refractive index, n₂, were calculated.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique

Zinc telluride thin films with different thicknesses have been deposited by electron beam gun evaporation system onto glass substrates at room temperature. X-ray and electron diffraction techniques have been employed to determine the crystal structure and the particle size of the deposited films. The stoichiometry of the deposited films was confirmed by means of energy-dispersive X-ray spectrometry. The optical transmission and reflection spectrum of the deposited films have been recorded in the wavelength optical range 450-2500 nm. The variation of the optical parameters, i.e. refractive index, n, extinction coefficient, k, with thickness of the deposited films has been investigated. The refractive index dispersion in the transmission and low absorption region is adequately described by the single-oscillator model, whereby the values of the oscillator strength, oscillator position, dispersion parameter as well as the high-frequency dielectric constant were calculated for different film thickness. Graphical representations of the surface and volume energy loss function were also presented.     

The relationship between refractive index-energy gap and the film thickness effect on the characteristic parameters of CdSe thin films

CdSe thin films were deposited on glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature and ambient pressure. The relationship between refractive index and energy bandgap was investigated. The film thickness effect on the structural, morphological, optical and electrical properties of CdSe thin films was investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibit polycrystalline nature with hexagonal structure and are covered well with glass substrates. The crystalline and surface properties of the films improved with increasing film thickness. The optical absorption studies revealed that the films are found to be a direct allowed transition. The energy bandgap values were changed from 1.93 to 1.87 eV depending on the film thickness. The electron effective mass (m_e^?/m_o), refractive index (n), optical static and high frequency dielectric constant (ε_o, ε_∞) values were calculated by using the energy bandgap values as a function of the film thickness. The resistivity of the films changed between 10⁶ and 10² Ω-cm with increasing film thickness at room temperature.     

Preparation and study of microstructures, optical properties and oscillator parameters of titanium (IV) oxide (TiO2) film

In this study, Titanium (IV) Oxide (TiO₂) film has been prepared and characterized by X-ray diffraction (XRD). The XRD pattern of TiO₂ film of anatase phase exhibit very sharp peaks at 25° and 47.85°. According to Scherrer??s formula the grain size of anatase (101) phase TiO₂ nananoparticle is 38.5 nm. The optical properties and constants of TiO₂ film of thickness (4 ??m) have been investigated at room temperature. The transmittance, reflectance and absorbance spectra are measured in the wavelength range (340?C900 nm). Optical constants of TiO₂ film are derived from the transmission spectra and the refractive index dispersion of the film. The oscillator energy, E ₀ dispersion energy, E _d , the static refractive index, n ₀, and other parameters have been determined by the single oscillator Wemple-DiDomenico method. This film can be used in the form of thin film in dye-sensitized solar cells.     

Infrared optical properties of Mn1.56Co0.96Ni0.48O4 thin films prepared by chemical solution deposition

～2 μm thick Mn_1.56Co_0.96Ni_0.48O₄ (MCN) films have been prepared on a Al₂O₃ substrate by the chemical solution deposition method. X-ray diffraction and microstructure analyses show good crystallization and the thickness of the films is 2.12 μm. Mid-infrared optical properties of MCN films have been investigated using transmission spectra and infrared spectroscopic ellipsometry. The optical band gap of the MCN film has been derived to be 0.64 eV by assuming a direct transition between valence and conduction bands. The optical constants and thickness of the thin films have been obtained by fitting the measured ellipsometric parameter data with the classical infrared model. The refractive index n of the MCN films decreases as the wavelength increases, but the extinction coefficient k monotonously increases in the wavelength range of 2–7 μm. The maximal n value is 2.63, and the maximal k value is only 0.024. The above results are instructive for the applications of MCN films in infrared detecting.     

Structural and optical analysis of 60Co gamma-irradiated thin films of polycrystalline Ga10Se85Sn5

The present study focuses on the effects of gamma irradiation on structural and optical properties of polycrystalline Ga₁₀Se₈₅Sn₅ thin films with a thickness of ～300?nm deposited by the thermal evaporation technique on cleaned glass substrates. X-ray diffraction patterns of the investigated thin films show that crystallite growth occurs in the orthorhombic phase structure. The surface study carried out by using the scanning electron microscope (SEM) confirms that the grain size increases with gamma irradiation. The optical parameters were estimated from optical transmission spectra data measured from a UV–vis-spectrophotometer in the wavelength range of 200–1100?nm. The refractive index dispersion data of the investigated thin films follow the single oscillator model. The estimated values of static refractive index n₀, oscillator strength E_d, zero frequency dielectric constant ε₀, optical conductivity σ_optical and the dissipation factor increases after irradiation, while the single oscillator energy E_o decreases after irradiation. It was found that the value of the optical band gap of the investigated thin films decreases and the corresponding absorption coefficient increases continuously with an increase in the dose of gamma irradiation. This post irradiation changes in the values of optical band gap and absorption coefficient were interpreted in terms of the bond distribution model.     

Thickness dependent optical properties of titanium oxide thin films

TiO₂ thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60°, 70°, and 75°, respectively. The whole spectra have been fitted by Forouhi–Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO₂ thin film have positive correlation to the film thickness. The refractive indices of TiO₂ thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO₂ thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO₂ thin film growth can be used to explain these phenomena.     

Optical characterization of poly (ethylene oxide)/zinc oxide thin films

The optical characterization of poly (ethylene oxide)/zinc oxide thin films has been done by analyzing the absorption spectra in the spectral wavelength region 380–800 nm using a ultraviolet-spectrophotometer at room temperature. Thin film polymer composites made of poly (ethylene oxide) (PEO) containing zinc oxide (ZnO) filler concentrations (0%, 2%, 6%, 10%, and 14%) by weight were used in this study. The optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The optical energy gap and other basic optical constants such as dielectric constants and optical conductivity were investigated and showed a clear dependence on the ZnO filler concentration. It was found that the optical energy gap for the composite films is less than that for the neat PEO, and that it decreases as the ZnO concentration increases. Enhancement of the optical conductivity was observed with increase in the ZnO concentration. Dispersion of refractive index was analyzed using the Wemple–DiDomenico single oscillator model. The refractive index (n), extinction coefficient (k), and dispersion parameters (E_o, E_d) were calculated for the investigated films.     

Effects of Pb addition and heat treatment on optical properties of thermally evaporated Ge1−xSe2Pbx thin films

Thin chalcogenide films of Ge_1−xSe₂Pb_x (x=0, 0.2, 0.4, 0.6 and 0.8) have been prepared by the thermal evaporation technique, from previously synthesized bulk samples. The X-ray diffraction showed the amorphous nature for the as-deposited films and the partially crystalline for the annealed films. The optical constants (the refractive index, n, and absorption index k) were determined for as-deposited and annealed Ge_1−xSe₂Pb_x films of different thicknesses by using spectrophotometeric measurements of the transmittance and reflectance at normal incidence in the spectral range 200-2500 nm. The obtained values of both n and k were found to be independent of the film thickness. The optical absorption edges are described using both the Urbach rule and the indirect transition. In transparent region, the spectral dependences of refractive index were interpreted in the frame of a single oscillator model.     

Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.     

Optical parameters of epitaxial GaN thin film on Si substrate from the reflection spectrum

A method has been proposed for determining the optical properties of a thin film layer on absorbing substrates. The film optical parameters such as thickness, refractive index, absorption coefficient, extinction coefficient and the optical energy gap of an absorbing film are retrieved from the interference fringes of the reflection spectrum at normal incidence. The envelopes of the maxima of the spectrum E_M and of the minima E_m are introduced in analytical forms to find the reflectance amplitudes at the interfaces and approximate values of the thin film refractive index. Then, the interference orders and film thickness are calculated to get accurate values of the needed optical parameters. There are no complex fitting procedures or assumed theoretical refractive index dispersion relations. The method is applied to calculate the optical properties of an epitaxial gallium nitride thin film on a silicon (1 1 1) substrate. Good agreement between our results and the published data are obtained.     

Thermal annealing effect of on optical constants of vacuum evaporated Se75S25−xCdx chalcogenide thin films

Chalcogenide glasses are interesting materials due to their infrared transmitting properties and photo induced effects exhibited by them. Thin films with thickness of 3000 Å of the glasses Se₇₅S_25−xCd_x with x=6, 8 and 10 at% prepared by melt quench technique were evaporated by thermal evaporation onto glass substrates under a vacuum of 10⁻⁶ Torr. The optical constants (absorption coefficient, refractive index and extinction coefficient) of as-prepared and annealed films have been studied as a function of photon energy in the wave length region 400-1000 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been found that the absorption coefficient and optical band gap increase with increasing annealing temperatures. The refractive index (n) and the extinction coefficient (k) were observed to decrease with increasing annealing temperature.