Effect of nano-metric changes on morphology and optical constants of TiO2 thin films

Titanium dioxide films of different thicknesses, ranging from 10 to 110 nm were deposited on glass substrate, at room temperature by physical vapor deposition method. Topography, roughness and crystallography of produced layers were determined by AFM and XRD methods respectively. Optical properties were measured by transmission spectroscopy in the spectral range of 300–1100 nm wave length range. The optical constants were obtained using Kramers-Kronig analysis of the reflectivity curves. It was found that film thickness plays an important role on the nanostructures as well as optical properties of layers and cause significant variations in behavior of thin titanium oxide films.     

A method for determining the optical constants of an absorbing film entering into the composition of a layered system

A matrix method of calculating the refractive index and the absorption factor of an absorbing film entering into the composition of a multilayer thin-film system (for example, of the dielectric-metal-dielectric type) from the measured transmission and reflection spectra of the system is proposed. The method is based on solution of the matrix equation for the layered system by the iterative method of continuous differential descent. The method developed was applied to determine the optical constants of a real silver film in the composition of a three-layer energetically efficient titanium dioxide-silver-titanium dioxide coating.     

Low-voltage driving phototransistor based on dye-sensitized nanocrystalline titanium dioxide thin films

Photo-gated transistors based on dye-sensitized nanocrystalline titanium dioxide thin film are established. A transistor-like transport behavior characterized by the linear increase, saturated plateau, and breakdown-like increase in the voltage-current curve is achievable with a low driven bias for the present device. The response current exhibits a linear dependence on the intensity of gated light, and the measured maximum photosensitivity is approximately 0.1 A/W. The dynamic responses for various light frequencies and their dependences on the load resistances are investigated as well. The cut-off frequency of ∼50 Hz is abstracted, indicating the potential application for economical and efficient light switch or optical communication unit. The DC photo-gated response is explained by the energy level diagram, and is numerically simulated by an equivalent circuit model, suggesting a clear correlation between photovoltaic and photoconductive behaviors as well as their optical responses.     

Optical,structural, and photocatalytic properties of the nanosized titanium dioxide films deposited in magnetron discharge plasma

The conditions of the optimum and controlled deposition of titanium dioxide nanolayers in the cylindrical gas discharge plasma of a magnetron having a unique design are found and described. The examination of the grown films by Raman spectroscopy is used to determine the conditions of deposition of the amorphous and polycrystalline phases of titanium dioxide. The films deposited on a cold substrate are amorphous, and the films deposited on a heated substrate consist of polycrystalline anatase. The evolution of the spectral lines of argon, oxygen, and titanium and the discharge voltage drop are studied as a function of the magnitude and the direction of changing the discharge current. The results obtained are shown to be applied for contactless optical monitoring. The refractive index of the films n is shown to have a nonlinear dependence on the layer thickness, and the layers that have a high photocatalytic activity and can be used to remove inorganic pollutants from the environment are shown to be grown.     

Thermally tunable optical constants of vanadium dioxide thin films measured by spectroscopic ellipsometry

Smart materials with reversible tunable optical constants from visible to near-infrared wavelengths could enable excellent control over the resonant response in metamaterials, tunable plasmonic nanostructures, optical memory based on phase transition and thermally tunable optical devices. Vanadium dioxide (VO₂) is a promising candidate that exhibits a dramatic change in its complex refraction index or complex dielectric function arising from a structural phase transition from semiconductor to metal at a critical temperature of 70 °C. We demonstrated the thermal controllable reversible tunability of optical constants of VO₂ thin films. The optical/dielectric constants showed an abrupt thermal hysteresis which confirms clearly the electronic structural changes. Temperature dependence of dielectric constants as well as optical conductivity of sputtered VO₂ thin films was also reported and compared to previous theoretical and experimental reports.     

A fibre-optic thermometric sensor based on the thermo-optic effect of titanium dioxide coatings

An experimental determination of the thermo-optic effect of titanium dioxide is described in which the test element is a thin film deposited onto the end face of an optical fibre. The film acts as an etalon. The reflectivity of titanium dioxide films was measured as a function of temperature experimentally over the range 20 °C to 500 °C, and modelled theoretically to yield a value of the thermo-optic coefficient of − 1.49 × 10⁻⁴ K⁻¹. The use of the data in the design of a thin-film optical fibre temperature sensor is described.     

椭偏光谱法研究溶胶-凝胶TiO2薄膜的光学常数

以钛酸丁酯为前驱体,采用溶胶-凝胶工艺成功制备了TiO₂薄膜.利用反射式椭圆偏振光谱仪测量了薄膜的椭偏参量Ψ和Δ,并用Cauchy模型对椭偏参数进行数据拟合,得到了薄膜的厚度和光学常数在380—800 nm的色散关系.用分光光度计测量了薄膜的反射率,并用干涉法计算薄膜的厚度;使用原子力显微镜观测了薄膜的表面微结构,分析讨论了不同退火温度处理的薄膜微结构与光学常数之间的关系.研究结果表明,Cauchy模型能较好地符合溶胶-凝胶TiO₂薄 关键词： 光学常数 2薄膜')" href="#">TiO₂薄膜 溶胶-凝胶 椭圆偏振     

Optical constants of thin oxide films on titanium

Thin oxide films on titanium formed by heating were studied by the ellipsometric method. To obtain the complex refractive index and film thicknesses, the ellipsometric measurements were performed by means of the immersing method: each sample was measured first in air and then in a liquid of known refractive index (in our case CCl₄). The optical constants and the oxide film thickness were computed by means of a computer from two pairs of ellipsometric values. To state the optical constants of clean titanium surface the graphic-computational method was proposed and applied. The measurements were carried out at two wavelengths on oxide films grown in air and dry oxygen by thermal oxidation at temperatures from 150 to 700 °C. It has been shown that when increasing the film thickness the refractive index of the film decreases, whereas the absorption coefficient is independent on the film thickness. Optical constants of oxide films growing in dry oxygen are smaller than those growing in air.     

In situ monitoring of laser-induced silicon oxidation

A low cost, computer-controlled, in situ monitor of laser-induced oxidation of c-Si is described. Both oxide thickness and processing temperature can be determined, simultaneously and with high spatial resolution, from the sample reflectivity and a knowledge of the temperature dependence of the optical constants of silicon and silicon dioxide (available in the literature).     

Determination of the anisotropy of the optical constants of electrochemically formed platinum oxide films by reflection spectroscopy and Kramers-Kronig analysis

Reflection spectroscopy in connection with Kramers-Kronig analysis was used to evaluate the complex optical constants of a thin anisotropic film of assumed uniaxial symmetry. The change in reflectivity of a platinum electrode, due to the formation of an oxide layer, was measured between 0.9 eV and 5.2 eV for parallel and perpendicular polarization. The corresponding phase-shifts were calculated from these data. The complex optical constants normal n?_n and tangential n?_t to the surface are now obtainable. The spectral dependence of the complex optical constants shows the expected anisotropic behaviour. The results are explained by means of a simple band model.     

Influence of impurities on the stability and electronic states of titanium dioxide in the form of anatase

The behavior of impurities (Si, Zr, Mg, Zn) in titanium dioxide with an anatase structure is investigated using the electron-density functional method (with due regard for the spin polarization). The influence of these impurities on the formation of oxygen vacancies and the specific features of the electronic structure is studied. It is demonstrated that the impurities can both improve and deteriorate the optical characteristics of titanium dioxide.     

Electrical and optical properties of titanium dioxide films

A method is described for producing insulating films of titanium dioxide by vacuum evaporation. Photomicrographs showing the growth of crystallites in the layer are presented, and X-ray and electron diffraction data are given. Sputtering regimes by means of which it is possible to produce compact layers of specific resistance 10¹³ ohm · · cm, dielectric strength 10⁶V/cm, and dielectric constant of 30 are given.By investigating optical density spectra and temperature variation of electrical conductivity for these specimens values were obtained for the optical and thermal forbidden band widths in titanium dioxide; these were 4.2 and 3.9 eV respectively. It was found that insulating films of titanium dioxide were completely transparent over a wide range of wavelengths from 300 to 1000 m. Using the same investigations in layers with electrical conductivity greater than 10^–13/ohm · · cm defects were discovered, which were connected with oxygen deficiency and gave three impurity energy levels in the forbidden band of titanium dioxide.In conclusion the authors would like to express their gratitude to Prof. K. V. Shalimova under whose guidance the work was executed.     

Spectrophotometric measurements on a titanium dioxide film with columnar-structure-induced anisotropy

A procedure combining spectrophotometry and measurements of reflectance and transmittance versus incident angles (R/T method) is developed to characterize an obliquely evaporated titanium dioxide (TiO₂) film. The R/T method determines the thickness and columnar orientation of the film. The film thickness can be measured with an uncertainty less than 10 nm. Optical constants of the film over a spectral range of 450 nm to 900 nm are obtained from spectrophotometric measurements with an accuracy around one percent.     

Synthesis and characterization of silica—titania core—shell particles

Abstract Nearly monodispersed particles of silica were prepared and coated with uniform layers of titanium dioxide in anatase phase by hydrolysis and condensation of titanium butoxide. The coating thickness could be altered by adjusting the concentration of reactants (titanium butoxide and water) and the amount of added silica particles. Different coating thicknesses were deposited and studied using optical absorption spectroscopy, electron microscopy and Fourier transform infra-red spectroscopy. It was found that silica particles of size 170 ±5 nm were coated with 23±5 nm thick layer of titanium dioxide. Alternatively titania particles of size 340±5 nm were synthesized by controlled hydrolysis of titanium ethoxide in the presence of sodium chloride. These particles were further coated with 135±5 nm thick layer of silica to investigate changes in properties after changing the shell material     

Optical constants of nanosized films of metal titanium

A new ellipsometric technique for optical measurements of the refraction and extinction indices and thickness of nanosized metal-titanium films in air is proposed and implemented. It is shown that the determination of optical constants of titanium films by measuring the ellipsometric parameters Ψ and Δ for a light beam incident upon the metal/substrate interface through the substrate of fused silica allows one to obtain optical constants of the metal, which correlate well with the results of the most reliable measurements performed in vacuum chambers. In this case, one can additionally determine the thickness and refractive index of the natural oxide film on the titanium surface. The obtained values of the optical constants of titanium, n ₂ = 3.42 ± 0.05 and k ₂ = 3.75 ± 0.05 (λ = 632.8 nm), agree well with the results of the measurements made in vacuum. The proposed technique makes it possible to measure the thicknesses of titanium films within the range 7–30 nm with an accuracy of 0.7 nm. The technique is tested on titanium films deposited onto fused silica substrates obtained by vacuum thermal evaporation. The possible error of determining the thickness due to various additional factors is estimated. The results of ellipsometric measurements of the thickness are compared with the data obtained from parallel measurements of electric resistance of the films.     

Thermal Stability of the Structure and Optical Properties of Nanostructured TIO2 Films

Russian Physics Journal - The structure and optical properties of titanium dioxide films have been studied during annealing from 100 to 400°C. The films were obtained by ion-plasma...     

Effect of titanium dioxide nanoparticles on polymer network formation

This work presents a study of the effect of nanoparticles on polymer composites to develop a powerful polymer dispersed liquid crystal materials. Tri propylene glycol diarcrylate/titanium dioxide nanocomposites were produced at various titanium dioxide fractions ranging between 0 and 1?wt%, through ultraviolet curing technique during 30?min. Different technics such as polarized optical microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis were used to characterize the samples. A dynamic swelling of polymer network was also investigated. The evolution of the acrylic double-bond conversion shows a decrease in the absorption intensity at 1637?cm^?1. It is noted that the conversion rate decreases from 0.1 to 1?wt% of titanium dioxide nanoparticles. An increase in glass transition temperature is observed by differential scanning calorimetry. The thermogravimetric analysis results reveal a highly improved thermal stability upon the addition of the reinforcing phase. The follow of kinetics swelling of polymer network shows a decrease of the swell ratio with the inclusion of titanium dioxide nanoparticles.     

Effects of Gold and Silver Nanoparticles on Optical Bistability of Titanium Dioxide Nanocolloid

Physics of the Solid State - In this study, titanium dioxide (TiO2) nanocolloid was synthesized through sol–gel method, and nonlinear optical properties were studied using z-scan method. The...     

Reststrahlspektrum und Eigenabsorptionskante von CdxCa1−xO

The reflectivity of Cd_xCa_1?xO mixed crystals prepared by sintering has been measured at 300 °K from 0.2 to 47μm. The Reststrahlenbands show the expected “one-mode” behavior. By Kramers-Kronig-analysis, the longitudinal and transversal optical mode frequencies, the static and high frequency dielectric constants, the damping constants and the Szigeti-effective charges were determined in dependence on the relative admixturex of Cadmium. While the bandgap and the optical lattice frequencies vary linearly withx, the effective charge shows a deviation from linearity.     

Optimization of process parameters of titanium dioxide films by response surfaces methodology

An efficient approach for determination of the optimum process parameters for titanium dioxide coatings by using second-order response surface model is presented and investigated experimentally. Thin films were prepared by electron-beam evaporation associated with ion-beam assisted deposition by using different control factors, including starting materials, working pressure, substrate temperature, deposition rate and annealing temperature. The factorial design of the experiment was established to meet the equipment conditions and to avoid affecting the results. The main effect between various factors and interactions are independent. The significant level of both the main effects and the interaction are observed by analysis of variance (ANOVA) approach. Based on the statistical analysis, the results have provided much valuable information on the relationship between various control factors and thin film properties. Besides the optimum optical constants and surface roughness of TiO₂ thin films were obtained in the range of each parameter level. The factorial prediction model for preparation parameters of thin film was also established.