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.     

Determination and analysis of dispersive optical constant of TiO2 and Ti2O3 thin films

Electron beam evaporation technique was used to prepare TiO₂ and Ti₂O₃ thin films onto glass substrates of thicknesses 50, 500 and 1000 nm for each sample. The structural investigations revealed that the as-deposited films are amorphous in nature. Transmittance measurements in the wavelength range (350-2000 nm) were used to calculate the refractive index n and the absorption index k using Swanepoel's method. The optical constants such as optical band gap , optical conductivity σ_opt, complex dielectric constant, relaxation time τ and dissipation factor tan δ were determined. The analysis of the optical absorption data revealed that the optical band gap E_g was indirect transitions. The optical dispersion parameters E_o and E_d were determined according to Wemple and Didomenico method.     

Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

Thin films of SnO₂ were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O₂. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap (E_g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.     

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 and acoustic properties of TeO2/WO3 glasses with small amount of additive ZrO2

The optical and acoustic properties of tellurite glasses in the system TeO₂/ZrO₂/WO₃ have been investigated. The refractive index at different wavelengths and the optical spectra of the glasses have been measured. From the refractive index and absorption edge studies for prepared glasses, the optical parameter viz; optical band gap (E_opt), Urbach energy, (ΔE), dispersion energy, E_d, and the average oscillator energy, E₀, have been calculated. Sound velocities were measured by pulse echo technique. From these velocities and densities values, various elastic moduli were calculated. The variations in the refractive index, optical energy gap and elastic moduli with WO₃ content have been discussed in terms of the glass structure. Quantitatively, we used the bond compression model for analyzing the room temperature elastic moduli data. By calculating the number of bonds per unit volume, the average stretching force constant, and the average ring size we can extract valuable information about the structure of the present glasses.     

Thermal annealing effect on structural and optical properties of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) thin films

Thin films of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) were prepared by thermal evaporation technique. Structural properties of these (as-prepared and annealed at 373, 423, 473 and 523 K) films were determined by X-ray diffraction and scanning electron microscopy, which showed that the grain sizes increasing by the annealing effect. The transmittance and reflectance of all Ch-diisoQ thin films were measured in the range 200–2500 nm. Some optical constants such as optical band gap (E _g ), dispersion energy (E _d ), single oscillator energy (E _o ) and optical dielectric constant at a higher frequency (ε _∞ ) were calculated at different annealing temperatures. The optical band gap of the samples is decreased with the increase of annealing temperatures due to the increasing of the π-dislocation. Finally, the values of the optical susceptibility, χ⁽³⁾, were found to be annealing dependence.     

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.     

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.     

Structure and optical analysis of Ta2O5 deposited on infrasil substrate

Electron beam gun technique was used to prepare Ta₂O₅ thin films onto infrasil substrates of thicknesses 333 and 666 nm. The structure characterization was investigated using X-ray diffraction patterns. Transmittance measurements in the wavelength range (240-2000 nm) were used to calculate the refractive index n and the absorption index k depending on Swanepole's method. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal one in the transparent region. The analysis of the optical absorption data revealed that the optical band gap E_g was indirect transition. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dispersion parameters (E_o and E_d) and the high frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration to the effective mass ratio were estimated according to the model of Spitzer and Fan. Graphical representation of the relaxation time as a function of photon energy was also presented.     

Structural, morphological and optical properties of CuAlS2 films deposited by spray pyrolysis method

The structural, morphological and optical properties of CuAlS₂ films deposited by spray pyrolysis method have been investigated. CuAlS₂ in the form of films is prepared at different deposition conditions by a simple and economical spray pyrolysis method. The structural, surface morphology and optical properties of the films were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and absorbance spectra, respectively. The films were polycrystalline, crystallized in a tetragonal structure, and are preferentially orientated along the (1 1 2) direction. Grain size values, dislocation density, and d% error of CuAlS₂ films were calculated. The optical band gap of the CuAlS₂ film was found to be 3.45 eV. The optical constants such as refractive index, extinction coefficient and dielectric constants of the CuAlS₂ film were determined. The refractive index dispersion curve of the film obeys the single oscillator model. Optical dispersion parameters E_o and E_d developed by Wemple-DiDomenico were calculated and found to be 3.562 and 12.590 eV.     

Effect of heat treatment on the optical and electrical transport properties of Ge15Sb10Se75 and Ge25Sb10Se65 thin films

The effect of heat treatment on the optical and electrical properties of Ge₁₅Sb₁₀Se₇₅ and Ge₂₅Sb₁₀Se₆₅ thin films in the range of annealing temperature 373-723 K has been investigated. Analysis of the optical absorption data indicates that Tauc's relation for the allowed non-direct transition successfully describes the optical processes in these films. The optical band gap (E_g^opt.) as well as the activation energy for the electrical conduction (ΔE) increase with the increase of annealing temperature (T_a) up to the glass transition temperature (T_g). Then a remarkable decrease in both the E_g^opt. and ΔE values occurred with a further increase of the annealing temperature (T_a>T_g). The obtained results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structure transformations. Furthermore, the deduced value of E_g^opt. for the Ge₂₅Sb₁₀Se₆₅ thin film is higher than that observed for the Ge₁₅Sb₁₀Se₇₅ thin film. This behavior was discussed on the basis of the chemical ordered network model (CONM) and the average value for the overall mean bond energy 〈E〉 of the amorphous system Ge_xSb₁₀Se_90−x with x=15 and 25 at%. The annealing process at T_a>T_g results in the formation of some crystalline phases GeSe, GeSe₂ and Sb₂Se₃ as revealed in XRD patterns, which confirms our discussion of the obtained results.     

Dielectric modelling of the transmittance spectra of thin As20S80 films

As₂₀S₈₀ thin films with different thicknesses (49.4-763.1 nm) were deposited on glass substrates using a thermal evaporation technique. Spectrophotometric measurements of the films' transmittance were taken in the wavelength range of 190-2500 nm. The transmission spectra were simulated with a computer model based on dielectric modelling to determine the optical constants and thicknesses of the films. The O'Leary-Johnson-Lim (OJL) models implemented in the commercial software programme SCOUT were used. Thicknesses obtained by the simulated method were correlated to the results obtained from a surface profiler technique. Optical parameters, such as the refractive index n, the absorption coefficient k, the optical band gap E_g, the high-frequency dielectric constant ε_∞, the Urbach energy E_U, the single-oscillator energy and the dispersion energy, were determined. The results indicated that the thickness effect can be separated into two distinct groups for films of thicknesses either less than or greater than 312 nm.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Ellipsometric characterization of PbI2 thin film on glass

The optical properties of polycrystalline lead iodide thin film grown on Corning glass substrate have been investigated by spectroscopic ellipsometry. A structural model is proposed to account for the optical constants of the film and its thickness. The optical properties of the PbI₂ layer were modeled using a modified Cauchy dispersion formula. The optical band gap E_g has been calculated based on the absorption coefficient (α) data above the band edge and from the incident photon energy at the maximum index of refraction. The band gap was also measured directly from the plot of the first derivative of the experimental transmission data with respect to the light wavelength around the transition band edge. The band gap was found to be in the range of 2.385±0.010 eV which agrees with the reported experimental values. Urbach's energy tail was observed in the absorption trend below the band edge and was found to be related to Urbach's energy of 0.08 eV.     

Determination and analysis of dispersive optical constants of CuIn3S5 thin films

CuIn₃S₅ thin films were prepared from powder by thermal evaporation under vacuum (10⁻⁶ mbar) onto glass substrates. The glass substrates were heated from 30 to 200 °C. The films were characterized for their optical properties using optical measurement techniques (transmittance and reflectance). We have determined the energy and nature of the optical transitions of films. The optical constants of the deposited films were determined in the spectral range 300-1800 nm from the analysis of transmission and reflection data. The Swanepoel envelope method was employed on the interference fringes of transmittance patterns for the determination of variation of refractive index with wavelength. Wemple-Di Domenico single oscillator model was applied to determine the optical constants such as oscillator energy E₀ and dispersion energy E_d of the films deposited at different substrate temperatures. The electric free carrier susceptibility and the ratio of the carrier concentration to the effective mass were estimated according to the model of Spitzer and Fan.     

基于透射光谱确定溶胶凝胶ZrO2薄膜的光学常数

基于溶胶凝胶ZrO₂薄膜的紫外/可见/近红外透射实验光谱,采用Swanepoel方法结合Wemple-DiDomenico色散模型,方便地导出了ZrO₂薄膜在200—1200nm波长范围内的光学常数,包括折射率、色散常数、膜层厚度、吸收系数及能量带隙.研究发现,溶胶凝胶ZrO₂薄膜具有高折射率(1.63—1.93,测试波长为632.8nm)、低吸收和直接能量带隙(4.97—5.63eV) 等光学特性,而且其光学常数对薄膜制备过程中的重要工艺 关键词： 光学常数 Swanepoel方法 2薄膜')" href="#">ZrO₂薄膜 热处理     

Optical studies of (NH4)2SO4 single crystal in the paraelectric phase

Transmittance and absorbance spectra of (NH₄)₂SO₄ single crystals along [010] direction were measured at different temperatures (296, 308, 318, 328 and 348 K) in the paraelectric phase. The absorption coefficient was computed and the analysis of the data revealed the existence of two optical transitions in (NH₄)₂SO₄ single crystals. The direct and indirect band gaps were shifted towards the longer wavelength with increasing temperature. The data on the allowed indirect transition was analyzed and interpreted in terms of two valence bands originated by spin orbit interaction and crystal field splitting. The momenta E_p were calculated as the difference between E_g1, the first valence to conduction band, and E_g2 for the second valence band at different temperatures. The results of extinction coefficient (k), the refractive index (n), and dielectric constants (ε) were also discussed and calculated as a function of wave length (λ). The heat treatment of the crystals proved that the variations of these optical parameters can be consequence of the internal microstructure changes caused by annealing.     

Optical and electrical properties of plasma-oxidation derived HfO2 gate dielectric films

High-k gate dielectric HfO₂ thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO₂ films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO₂ film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.     

Switching phenomenon and optical properties of Se85Te10Bi5 films

Se₈₅Te₁₀Bi₅ films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se₈₅Te₁₀Bi₅ films were amorphous. Electrical conduction activation energy (ΔE_σ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se₈₅Te₁₀Bi₅ films reveals that it is typical for a memory switch. The switching voltage V_th increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of V_th is found to be 0.325 eV. The switching phenomenon in amorphous Se₈₅Te₁₀Bi₅ films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se₈₅Te₁₀Bi₅ films. Allowed non-direct transitions with an optical energy gap (E_g^opt) of 1.33 eV have been obtained. ΔE_σ is almost half the obtained value of E_g^opt, which suggested band to band conduction as indicated by Davis and Mott.     

Influence of atomic hydrogen annealing on the optical properties of vacuum-deposited a-Si:H films

The influence of atomic hydrogen annealing on the optical parameters of a-Si:H films was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200-3000 nm. In this annealing, the deposition of a thin layer and treatment with atomic hydrogen were repeated alternately, where the thickness of the thin cyclic layer, d_cyc, and the treatment time of each cycle, t_ca, were kept fixed for each sample. A series of different samples with average thickness of 0.5 μm and different d_cyc and t_ca were prepared. It was found that the refractive index, n, and the optical energy gap, E_g, increase as the treatment time, t_ca, increases from 0 to 60 s, while at t_ca=120 s both n and E_g decrease. Also, both the refractive index and the optical energy gap decrease with increasing the relative diffusion length of hydrogen, √t_ca/d_cyc from 0.39 to 0.77. The widening of E_g is due to the structural relaxation resulting from impingement of atomic hydrogen on the growing surface. Thus, a good-quality a-Si:H with Urbach parameter 65 mev and optical energy gap of 1.78 eV was successfully prepared.