Effect of cycle numbers on the structural,linear and nonlinear optical properties in Fe2O3 thin films deposited by SILAR method

Fe₂O₃ thin films were deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method onto glass substrates at different cycle numbers to investigate structural, linear and nonlinear optical properties. X-Ray Diffraction (XRD) analysis revealed that the Fe₂O₃ thin films have a non-crystalline nature. The morphological properties of the films were investigated by Field Emission-Scanning Electron Microscopy (FE-SEM) and the results show that the films’ surfaces are porous. The linear and nonlinear optical parameters were evaluated and analyzed by using transmittance and absorbance measurements. For these measurements, UV–Vis spectroscopy at room temperature was used. The refractive index values were calculated in the range of 1.45–3.23 for visible region (400–700 nm). Obtained results reveal that direct optical band gap changed between 2.62 and 2.68 eV and indirect optical band gap changed between 1.67 and 1.77 eV. Additionally, optical electronegativity, optical dielectric constants, surface and volume energy loss functions, nonlinear refractive index, linear optical susceptibility, third-order nonlinear optical susceptibility, optical and electrical conductivity, and loss tangent values were calculated and discussed in detail. It was found that each parameter studied is dependent on the cycle numbers. Also, it can be stated that Fe₂O₃ thin films are promising candidate for solar cells and optoelectronic device technology.     

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 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.     

Photoinduced changes in optical properties of Ga-Sb-Ge-Se glasses

The kinetics of photoinduced effects on Ga₅Sb₁₀Ge₂₅Se₆₀ thin film exposed to continuous wave laser radiations are studied as a function of exposure time and laser intensity. The transmission and reflection spectra of thin films before and after exposure are investigated. The optical band gap and the refractive index are derived from the above spectra. Generalized Miller's rule and linear refractive index are used to find the nonlinear susceptibility and nonlinear refractive index of the thin films. The studies show a red shift in the band gap with increase in exposure time and laser power which is attributed to the photoinduced darkening in the films.     

An optical study of vacuum evaporated amorphous Ge<Subscript>20</Subscript>Te<Subscript>80−<Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films using transmission and reflection spectra

The present paper reports the effect of Bi addition on the optical behavior (optical band gap and refractive index) of Ge₂₀Te_80?x Bi _x (where x=0, 1.5, 2.5, 5.0) glassy alloys by analyzing the transmission and reflection spectra of their thin films in the 900–2400 nm range. Films are deposited on glass substrate using a thermal evaporation technique under vacuum. Various optical parameters viz. refractive index, extinction coefficient, absorption coefficient, optical band gap, etc. are determined and the effect of Bi incorporation on these parameters is studied. The refractive index has been found to increase with increasing Bi content over the entire spectral range and this behavior is due to the increased polarizability of the larger Bi atomic radius (1.46 Å) compared to Te atomic radius (1.36 Å). Dispersion energy, E _d , average energy gap, E ₀ and static refractive index, n ₀ is calculated using Wemple–DiDomenico model. Optical band gap is estimated using Tauc’s extrapolation and is found to decrease from 0.86 to 0.73 eV with the Bi addition. This behavior of the optical band gap is interpreted in terms of the electronegativity difference of the atoms involved and the cohesive energy of the system.     

Nonlinear optical absorption in Bi3TiNbO9 thin films using Z-scan?technique

Bi₃TiNbO₉ (BTN) thin films with layered perovskite structure were fabricated on fused silica by pulsed laser deposition. The XRD pattern revealed that the films are single-phase perovskite and highly (00l) textured. Their fundamental optical constants, such as band gap, linear refractive index, and linear absorption coefficient, were obtained by optical transmittance measurements. The dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The nonlinear optical absorption of the films was investigated by single beam Z-scan method at a wavelength of 800 nm with laser duration of 80 fs. We obtained the nonlinear absorption coefficient β=1.44×10⁻⁷ m/W. The results show that the BTN thin films are promising for applications in absorbing-type optical devices.     

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.     

Structure and optical properties of chemically synthesized titanium oxide deposited by evaporation technique

Titanium oxide inorganic ion exchange material was synthesized by hydrolysis with water and ammonia solution. Structural feature of the synthesized titanium oxide was analyzed using X-ray diffraction, X-ray fluorescence and infrared spectrometer technique. Tentative formula of titanium oxide was determined and written as TiO₂·0.58H₂O. Titanium oxide films were deposited on glass substrates by means of an electron beam evaporation technique at room temperature from bulk sample. The films were annealed at 250, 350, 450, and 550 °C temperatures. Transmittance, reflectance, optical energy gap, refractive index and extinction coefficient were investigated. The transmittance values of 85% in the visible region and 88% in the near infrared region have been obtained for titanium oxide film annealed at 550 °C. Kubelka-Munk function was used to evaluate the absorption coefficient which was used to determine the optical band gap. It was found that the optical band gap increases with increasing annealing temperature whereas the refractive index and extinction coefficient decreases.     

Linear and nonlinear optical properties of hydrogenated CdO thin films

The linear and nonlinear optical properties of a CdO film post-annealed in a hydrogen atmosphere for 30 min (CdO:H) were studied. The prepared CdO and CdO:H films were characterized by X-ray diffraction and UV-VIS-NIR absorption spectroscopy. Experimental data indicated that annealing in an H₂ atmosphere slightly compresses the CdO unit cell and widens the energy gap of CdO by about 3% relative to a nonhydrogenated film. This effect can be explained by the Burstein-Moss energy effect. The nonlinear absorption and nonlinear refractive index coefficients were determined and found to be higher than the values previously determined for nonhydrogenated CdO.     

Optical characterization of CuIn5S8 crystals by ellipsometry measurements

Optical properties of CuIn₅S₈ crystals grown by Bridgman method were investigated by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficients were obtained from the analysis of ellipsometry experiments performed in the 1.2–6.2 eV spectral region. Analysis of spectral dependence of the absorption coefficient revealed the existence of direct band gap transitions with energy 1.53 eV. Wemple–DiDomenico and Spitzer–Fan models were used to find the oscillator energy, dispersion energy, zero-frequency refractive index and high-frequency dielectric constant values. Structural properties of the CuIn₅S₈ crystals were investigated using X-ray diffraction and energy dispersive spectroscopy analysis.     

Structural, optical and magnetic properties of Nd-doped BiFeO3 thin films prepared by pulsed laser deposition

Nd-doped BiFeO₃ thin films were grown by pulsed laser deposition on quartz substrate and their structural, optical and magnetic properties have been studied. X-ray diffraction analysis revealed that Nd addition caused structural distortion even with 5% of Nd concentration, additional secondary phase appeared in all samples but its intensity was greatly reduced with Nd addition. Doping-induced variations in texture and structure modifying both magnetic and optical properties of BiFeO₃ thin films. The energy band gap decreases while the refractive index increases with addition of Nd³⁺ in BiFeO₃ for Bi³⁺. These variations in energy band gap and refractive index have been explained on the basis of density of states and increase in disorders in the system. All the samples were found to exhibit ferromagnetism at room temperature and the saturation magnetization increases with the increase in structural distortion with addition of Nd. Finally, Nd-doping modifies the physical properties of BiFeO₃ in comparison to undoped BiFeO₃ thin films.     

Structural and optoelectronic properties of amorphous GaN thin films

Amorphous gallium nitride (a-GaN) thin films were deposited on glass substrate by electron beam evaporation technique at room temperature and high vacuum using N ₂ as carrier gas. The structural properties of the films was studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). It was clear from XRD spectra and SEM study that the GaN thin films were amorphous. The absorbance, transmittance and reflectance spectra of these films were measured in the wavelength range of 300–2200 nm. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct band gap of E _g = 3:1 eV. The data analysis allowed the determination of the dispersive optical parameters by calculating the refractive index. The oscillator energy E ₀ and the dispersion energy E _d, which is a measure of the average strength of inter-band optical transition or the oscillator strength, were determined. Electrical conductivity of a-GaN was measured in a different range of temperatures. Then, activation energy of a-GaN thin films was calculated which equalled E _a = 0:434 eV.     

Structural and optical properties of thermally evaporated 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile thin films

The structural and optical properties of as-deposited and γ-rays irradiated 2-(2,3-dihydro-1,5dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films have been reported. The structural properties of as-deposited and γ-rays irradiated DOPNA thin films are characterized by Fourier transformation infrared, X-ray diffraction and transmission electron microscope techniques. The transmittance, T(λ), and reflectance, R(λ), are measured at the normal incidence of light by a double beam spectrophotometer in the wavelength range 200-2200 nm. The refractive and absorption indices have been calculated. The dispersion parameters such as dispersion energy, oscillator energy and dielectric constant at high frequency are evaluated. The data of the absorption coefficient are analyzed in order to determine the type of inter-band electronic transitions and the optical band gap of the films. Other optical absorption parameters, namely, the extinction molar coefficient, oscillator strength and the electric dipole strength, are also calculated.     

Derivation of the optical constants of spin coated CeO2-TiO2-ZrO2 thin films prepared by sol-gel route

Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate, Ce(NO₃)₆(NH₄)₂, titanium butoxide, Ti[O(CH₂)₃CH₃]₄, and zirconium propoxide, Zr(OCH₂CH₂CH₃)₄, were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO₂-TiO₂-ZrO₂ gel to study the decomposition and phase transition of the gel. For molecular, structural, elemental, and morphological characterization of the films, Fourier Transform Infrared (FTIR) spectral analysis, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), cross-sectional scanning electron microscopy (SEM), and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index, extinction coefficient, band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index, extinction coefficient, and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E_g≈2.82±0.04 eV for indirect transition.     

Optical properties of Tl2In2Se3S layered single crystals

The optical properties of Tl₂In₂Se₃S layered single crystals have been analyzed using transmission and reflection measurements in the wavelength region between 500 and 1100 nm. The optical indirect transitions with a band gap energy of 1.96 eV and direct transitions with a band gap energy of 2.16 eV were determined from analysis of absorption data at room temperature. Dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-effective-oscillator model. The refractive index dispersion parameters – oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index – were found to be 4.67 eV, 45.35 eV, 1.38 × 10¹⁴ m ^{? 2} and 3.27, respectively. Transmission measurements were also performed in the temperature range 10–300 K. As a result of temperature-dependent transmission measurements, the rate of change in the indirect band gap with temperature, i.e. γ = ?5.6 × 10^?4 eV/K, and the absolute zero value of the band gap energy, E _gi(0) = 2.09 eV, were obtained.     

Investigation of nonlinear optical parameters of zinc based amorphous chalcogenide films

Third order nonlinear optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films have been investigated using single beam transmission z-scan technique at 1064 nm of Nd:YAG laser. Measurement of optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films prepared by thermal evaporation technique has been made. X-ray diffraction patterns of chalcogenide films confirm the amorphous nature. Optical band gap (E_g) has been estimated using Tauc's plot method from transmission spectra that is found to decrease with increase in content due to valence band broadening and band tailing the system. Nonlinear refractive index (n₂), nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ³) of chalcogenide films have been estimated. Self-focusing effect has been observed in closed aperture and reverse saturable absorption in open aperture scheme. Limiting threshold and dynamic range have been calculated from optical limiting studies. The increase in nonlinearity with increase in Zn content has been observed that is understood to be due to decrease in band gap on Zn doping. High nonlinearity makes these films a potential candidate for waveguides, fibers and two photon absorption in optical limiters.     

Influence of Ge addition on the optical properties of As40Se50Ge10 thin film probed by spectroscopy techniques

The thin films of As₄₀Se₆₀ and As₄₀Se₅₀Ge₁₀ were prepared on glass substrates by thermal evaporation method with thickness 1000 nm. The prepared films were amorphous in nature which was confirmed through X-ray diffraction. The chemical composition and the surface picture were obtained from energy dispersive X-ray analysis and Scanning Electron Microscopy analysis. The transmission data of the two films were collected in the wavelength range 400–1000 nm. The transmission percentage is found to be decreased whereas the absorption coefficient is increased with the Ge addition. The addition of Ge into As₄₀Se₆₀ is found to increase the refractive index and the extinction coefficient of As₄₀Se₅₀Ge₁₀ thin film. The decrease in optical band gap is explained on the basis of increase in density of states and disorderness due to Ge addition. The optical absorption in the film is due to allowed indirect transition, and the homopolar bond density is increased with Ge addition. The Raman shift observed in the two films clearly supports the optical changes due to Ge addition.     

Optical properties of amorphous HF–In–Zn–O thin films estimated from transmission spectra

Amorphous and flat (<1 nm roughness) Hf–In–Zn–O thin films were prepared by radio frequency (rf) magnetron sputtering method at room temperature (RT) and at 300 °C substrate temperature. The crystal structure and surface morphology were investigated by high resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM), respectively. Optical properties of these films were obtained from the UV–VIS–NIR transmission spectra, at normal incidence, over the 200–2000 nm spectral range. Swanepoel's method was used to calculate the thickness and the refractive index of the films. The dispersion of refractive index was obtained in terms of the single-oscillator Wemple–DiDomenico model. The optical absorption edge was described using the direct transition model proposed by Tauc. The film deposited at higher substrate temperature had lower optical band gap, higher refractive index, higher oscillator strength and energy of the effective dispersion oscillator. Optical characterization shows that films become more stable, relaxed and rigid at higher substrate temperature.     

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.     

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.