Transparent high refractive index nanocomposite thin films

This work reports the preparation of acetic acid-modified TiO₂ nanoparticles by sol–gel synthesis method. The nanoparticles can be incorporated directly into the polymer matrix to form transparent high refractive index nanocomposite thin films. The result shows that increasing the titania content in the hybrid nanocomposite thin films can significantly increase the refractive index. Hybrid nanocomposite thin film with refractive index value of 2.38 had been prepared. All prepared films also exhibit excellent optical transparency in the visible region.     

Optical band gap and refractive index of c-BN thin films synthesized by radio frequency bias sputtering

Boron nitrogen (BN) films with the different cubic phase content were deposited on Si and fused silica substrates by radio frequency bias sputtering from a hexagonal BN target by using a two-stage deposition process. The BN films were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection measurements. The optical absorption coefficient and the refractive index n were calculated from the transmittance and reflection spectra. With increasing the c-BN content the absorption edge shifts to the higher energy, indicating that the optical band gap of the BN films increases with cubic BN content. The optical absorption behavior of BN films shows characteristics of amorphous materials. The dependence of on the photon energy was fitted by the Urbach tail model and the band-to-band transition model at the two different energy regions, and the optical band gap of the BN films were obtained from the fits. In addition, the refractive index indicates obvious difference for the BN films with different cubic phase content.     

Temperature dependence of the band gap, refractive index and single-oscillator parameters of amorphous indium selenide thin films

InSe thin films are obtained by evaporating InSe crystal onto ultrasonically cleaned glass substrates under pressure of 10⁻⁵ Torr. The structural and compositional analysis revealed that these films are of amorphous nature and are atomically composed of 51% In and 49% Se. The reflectance and transmittance of the films are measured at various temperatures (300–450 K) in the incident photon energy range of 1.1–2.1 eV. The direct allowed transitions band gap – calculated at various temperatures – show a linear dependence on temperature. The absolute zero value band gap and the rate of change of the band gap with temperature are found to be (1.62 ± 0.01) eV and −(4.27 ± 0.02) × 10⁻⁴ eV/K, respectively. The room temperature refractive index is estimated from the transmittance spectrum. The later analysis allowed the identification of the static refractive index, static dielectric constant, oscillator strength and oscillator energy.     

Measuring the refractive index of thin liquid films with a spectrometer

We discuss the manufacture and use of a prism pair to measure the refractive index of thin liquid films with a spectrometer. The method requires only a drop of liquid and is accurate to ~2 x 10(-4).     

Determination of refractive index, thickness, and the optical losses of thin films from prism-film coupling measurements

We present a method of analysis of prism-film coupler spectroscopy based on the use of transfer matrix and genetic algorithm, which allows the simultaneous determination of refractive index, thickness, and optical losses of the measured layer.     

氧分压对BiFeO_3薄膜能带结构和折射率的影响及其光学表征

采用射频磁控溅射在玻璃衬底上制备了BiFeO3薄膜,通过透射光谱和椭圆光谱研究了氧分压对BiFeO3薄膜能带结构及光学性能的影响。结果表明,BiFeO3薄膜在近红外区具有良好的透射性,透射率均在80%以上,其禁带宽度Eg=(2.79±0.03)eV。随着氧分压的增大,BiFeO3薄膜中氧缺陷及氧缺陷能级减少,导致透射率和禁带宽度均增大。同时发现,OJL色散模型与Cauchy色散模型的叠合能够对BiFeO3薄膜的椭圆光谱进行很好的描述。     

Extraction of the refractive index profile of thin transparent conductive oxide films from the analysis of reflectance optical spectra

In the direction of growth of fabricated films, the material near the free surface as well as the interface with the substrate exhibits properties which are different from those of the material in the bulk. The resulting spatial inhomogeneity of the refractive index influences positions and values of the extrema of optical spectra. We exploit this to derive the profile of the refractive index by developing a theoretical approach. In the calculations, taking the derived profile into account, we attain a good reproduction of the experimental Transmittance and Reflectance spectra from approximately 1 to 4 eV, the region of relatively weak refractive-index dispersion.     

Extraction of complex refractive index of absorbing films from ellipsometry measurement

Numerical extraction of complex refractive index of an unknown absorbing layer inside a multilayer sample from ellipsometry measurement is discussed. The approach of point by point extraction considering all points of spectroscopic data as independent data points is investigated. This problem has typically multiple solutions and the standard method consisting in fitting calculated to experimental point is likely to converge to a wrong solution if a precise guess value is not given. An alternate method is proposed, based on the determination of contours of the ellipsometric function, to provide all solutions in an as extended as wanted range of complex refractive index values. The method is tested through different kinds of sample examples. Errors relative to any of the parameters used in the sample model are calculated and discussed. This method should be helpful in many practical cases of ellipsometry data interpretation.     

Measurement of the physical thickness and refractive index of thin epitaxial garnet films

A technique for the measurement of refractive index and physical film thickness of epitaxial garnet films is described which utilizes variable wavelength measurements. Experimental results are presented for gadolinium gallium garnet substrates and two different bubble domain film compositions. From these results, it is concluded that the technique is not applicable to wafers with films on both sides due to the differences in film thickness of the two films. For single sided wafers, the refractive index can be determined with an accuracy of ±0.3 percent.     

硼碳氮薄膜的脉冲激光沉积及其光学性能

采用脉冲激光沉积技术,在Si(100)和石英基片上制备了硼碳氮薄膜(BCN)。利用X射线衍射(XRD),傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和紫外-可见分光光度计对BCN薄膜进行了表征,研究了激光能量密度对BCN薄膜沉积速率、组分、结构和光学性能的影响。FTIR和XPS分析结果表明BCN薄膜中包含B-C,C-N和N-B化学键,说明实现了B、C和N的原子级化合。当激光能量密度从1 J/cm2增加到6 J/cm2时,BCN薄膜的沉积速率加快,N含量由7.2%增加到15%,光学禁带宽度(Eg)从4.02 eV降低到3.82 eV,Eg的降低主要与BCN薄膜中碳含量的增加有关。     

Structural and optical properties of high refractive indices lead vanadate thin films

Glasses with the chemical formula xWO₃–50PbO–(50 − x)V₂O₅, (0 ≤ x ≤ 10 mol%) were prepared by the usual melt quenching technique. FTIR analysis revealed that, the incorporation of WO₃ into the lead-vanadate network increases the number of bridging oxygens, and replaces low-coordinated structural units such as PbO₄, and VO₄ with higher coordinated structural units WO₆ and VO₅ which increases the number of bonds and the average cross-link density. Thin films of these glasses onto quartz substrates have been obtained by thermal evaporation technique. Based only on the measured transmittance spectra in the wavelength range 200–2500 nm, both the film thickness and the complex index of refraction have been calculated precisely. The absorption edge was shifted toward the long wavelength side (i.e. red shift of the optical band gap) as the WO₃ content increases. The dispersion of the refractive index was discussed in terms of the single oscillator model. The allowed non-direct transitions successfully describe the absorption mechanism in these films. Based on generalized Miller's rule, the third-order non-linear optical susceptibility χ⁽³⁾ has been investigated. The obtained values of χ⁽³⁾ values are rather large, indicating that the films under study are interesting materials for non-linear optical devices.     

Effect of refractive index on the measurement of optical properties in turbid media

Continuous-wave measurement-based methods offer a rapid cost-effective way to determine optical properties in turbid media. This method requires a measure of the refractive index of the medium, which is often unknown a priori. Whereas previous studies have reported that the refractive index has little impact on the measurement of optical properties, here we show a significant effect of refractive indices on measurements, using both simulations and experiments. In addition we propose a noniterative method to determine the refractive index of the medium. This method can also provide an optimal initial guess of the optical properties for the standard iterative method for determining optical properties in turbid media. Our method is confirmed by simulations and experiments with latex spheres and Intralipid suspensions.     

Influence of gamma irradiation on the refractive index of Fe-doped barium titanate thin films

Polycrystalline Fe-doped barium titanate (Fe-doped BaTiO₃) thin films were grown by thermal decomposition of the precursors deposited from a sol-gel system onto quartz substrates. The changes in the transmittance spectra induced by gamma irradiation on the Fe-doped BaTiO₃ thin films were quantified. The values for the optical energy band gap were in the range of 3.42-3.95 eV depending on the annealing time. The refractive index of the film, as measured in the 350-750 nm wavelength range was in the 2.17-1.88 range for the as prepared film, and this increased to 2.34-1.95 after gamma irradiation at 15 kGy. The extinction coefficient of the film was in the order of 10⁻² and increased after gamma irradiation. We obtained tuneable complex refractive index of the films by exposure to various gamma rays doses.     

Spectral dependence of the complex refractive index of GeS2 chalcogenide glass thin films

Abstracts are not published in this journal     

Vacuum deposition of chiral sculptured thin films with high optical activity

We present the technique of bideposition to realize thin-film helicoidal bianisotropic mediums (TFHBM's) that exhibit high optical activity. We show, by experiment as well as by simulation, that the optical rotation produced by these chiral sculptured thin films is roughly proportional to the square of the local linear birefringence. Experimental measurements on bideposited TFHBM's of titanium oxide yield a typical value of 5 degrees /mum for the effective specific rotation in the short-wavelength regime; the corresponding value determined for the standard unideposited TFHBM's is 1 degrees /mum. Both types of TFHBM's are highly optically active in comparison with quartz, fluorite films, and cholesteric liquid crystals. Bideposited TFHBM's will lend themselves to many different types of optical devices.