椭偏与光度法联用精确测定吸收薄膜的光学常数与厚度

介绍了一种同时利用椭偏仪和分光光度计精确测量薄膜光学常数的方法, 并详细比较了该方法与使用单一椭偏仪拟合结果的可靠性.采用可变入射角光谱型椭偏仪（VASE）表征了250—1700 nm波段辉光放电法沉积的类金刚石薄膜,研究发现当仅用椭偏参数拟合时,由于厚度与折射率、消光系数的强烈相关性,无法得到吸收薄膜光学常数的准确解.如果加入分光光度计测得的透射率同时拟合,得到的结果具有很好的惟一性.该方法无需设定色散模型即可快速拟合出理想的结果,特别适合于确定透明衬底上较薄吸收膜的光学常数. 关键词： 光学常数 光谱型椭偏仪 吸收薄膜 透射率     

Method of envelopes for studying a two-film system on a reflecting substrate

For determining the optical constants and the thickness of thin films (including strongly absorbing films) by the spectrophotometric method, we propose to deposit them on intermediate films formed on strongly reflecting substrates. Due to this, an interference pattern depending on the optical constants and the thickness of the film under study will be observed in the reflectance spectrum. The method of envelopes of the extrema in the reflectance spectrum that is based on the iterative approach is developed for studying two-film systems.     

Simple method for the complete optical analysis of very thick and weakly absorbing films

In this paper a method for the determination of the thickness and spectral dependences of the optical constants characterizing very thick and weakly absorbing thin films located on nonabsorbing substrate is presented. Within the framework of this method the positions and values of the extrema in the spectral dependences of the reflectance and transmittance are utilized for evaluation the values of the optical parameters mentioned above. The main advantage of the method is that the values of the optical parameters can be determined by means of explicite formulae with relatively high accuracy. The method is utilized for the complete optical analysis of magnetic garnet films.     

Die Bestimmung der optischen Konstanten dünner Schichten in der Nähe der Plasmafrequenz aus Kurvenfeldern konstanter Transmission

A method is given to determine the optical constants and the foil thickness of thin absorbing films by means of curves of constant transmission. The influence of the experimental error on the accuracy is pointed out. The method is applied to the determination of the optical constants of silver foils of about 600 Å thickness between 270 and 650 °K in the wavelenght interval 3,000 to 3,600 Å.     

Optical constants of nanostructured layers of copper,nickel, palladium,and some oxides in the UV and visible spectral regions

It is found that a significant spread in the optical constants of metals reported by different authors is caused by differences in the sample preparation methods, measurement conditions, and methods of calculation of sought parameters, as well as by the oxidation effect. It is shown that the optical constants of metals in films 80–120 nm thick on silicon substrates with scattering below 10⁻⁴ are determined with minimal errors. The reflectance of these mirrors calculated from the optical constants found by the most accurate ellipsometric method coincides with the experimental value within the measurement accuracy. Low values of k(λ) obtained for thin layers in some works using the methods based on the measurement of the coherent transmittance and regular reflectance are explained by disregarded scattering and luminescence. The spectra of the imaginary part of the complex refractive index of copper, nickel, and copper oxide determined by us by the proposed methods for thin nanostructured layers taking into account the scattering and luminescence coincide with the most correct data for thick films in the spectral range of 325–633 nm. For thin palladium and palladium oxide layers, the variations in k(λ) are caused by the oxidation of metal granules and disregarded luminescence for thick oxide layers in the long-wavelength spectral region. The maximal difference in the imaginary part of the complex refractive index of copper and nickel for thin nanostructured layers are observed in the region of plasmon resonances, whose positions and amplitudes depend on the degree of asphericity, the shape, and the degree of order of particles and their aggregates, which shift the plasmon resonances of films to longer wavelengths with respect to spherical particles.     

Measurement of optical constants of thin polymer films using spectrally resolved white light interferometry

Using the spectrally resolved white light interferometry we present our experimental results on the measurement of the optical constants of thin polymer films coated on a transparent substrate. As an extension to our previous work (J. Opt. Soc. Am. B12, 1559 (1995)) on thick glass plates, we have shown here that this technique can be effectively applied to very thin polymer films also. We have improved the accuracy of our results by using the Sellmeier dispersion formula for fitting the data. From the width and position of the zero-order fringe and the frequency of modulations in the white light spectrum, the refractive indexn(λ) and thicknesst of the thin polymer films are calculated. To study the accuracies involved in the technique, PVA, PMMA and PS films of varied thicknesses are coated on glass plates and the measured values are compared with ellipsometer studies.     

椭偏精确测定透明衬底上吸收薄膜的厚度及光学常数

椭偏仪难以精确测量透明衬底上吸收薄膜光学常数的原因:1)衬底的背面反射光为非相干光, 它的存在会极大的增加拟合难度; 2)衬底光学常数(折射率和消光系数)的差异会影响测量的准确性, 而且会在吸收薄膜的光学常数中表现出来, 需要单独测量其光学常数; 3)厚度与光学常数之间呈现强烈的关联性. 针对以上三个问题, 选择石英玻璃、载玻片、盖玻片和普通浮法玻璃作为研究对象. 采用折射率匹配法消除上述衬底背面反射光的影响. 结果显示, 折射率匹配法能够有效消除折射率在1.43-1.64、波长范围为190-1700 nm波段的石英、浮法玻璃等透明衬底的背面反射光. 之后, 通过拟合椭偏参数ψ和垂直入射时的透过率T₀ 分别得到以上衬底的折射率和消光系数. 拟合得到的结果与文献报道的趋势一致. 最后, 采用椭偏参数和透过率同时拟合的方法(SE+T法)得到类金刚石薄膜(沉积在石英玻璃上)和非晶硅薄膜(沉积在载玻片、盖玻片上)光学常数和厚度的准确解.     

椭偏透射法测量氢化非晶硅薄膜厚度和光学参数

针对多角度椭偏测量透明基片上薄膜厚度和光学参数时基片背面非相干反射光的影响问题,报道了利用椭偏透射谱测量等离子增强化学气相沉积法(PECVD)制备的a-Si:H薄膜厚度和光学参数的方法,分析了基片温度T_s和辉光放电前气体温度T_g的影响.研究表明,用椭偏透射法测量的a-Si:H薄膜厚度值与扫描电镜(SEM)测得的值相当,推导得到的光学参数与其他研究者得到的结果一致.该方法可用于生长在透明基片上的其他非晶或多晶薄膜. 关键词： 椭偏测量 透射法 光学参数 氢化非晶硅薄膜     

Vacuum ultra-violet spectroscopic ellipsometry study of sputtered BeZnO thin films

This paper reports on a systematic investigation of the optical properties of BeZnO thin films fabricated by radio frequency reactive magnetron sputtering technique using vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). The thicknesses and optical constants of the thin films were determined in the wavelength range 138–1650 nm, using VUV-SE through the Tauc–Lorentz and Gaussian models. Refractive indices and extinction coefficients of the thin films were determined to be in the range n = 1.58–1.99 and κ = 1.0 × 10⁻²⁷–0.37, respectively. The absorption coefficient and the optical bandgap energy were then calculated. Measurement of the polarized optical properties reveals a high transmissivity (>90%) and very low absorptivity (<4%) for BeZnO films in the visible and near infrared regions at different angles of incidence. From the angle dependence of the p-polarized reflectivity we deduced a Brewster angle of about 58.5°.     

Effect of the structure of smooth copper surfaces on the accuracy of determination of the optical constants of copper

The accuracy of determination of the optical constants of smooth copper surfaces produced by different technologies is analyzed, with particular attention paid to the consideration of the influence of scattered radiation (which is ignored by many authors) on the retrieval of the optical constants of copper surfaces from reflected radiation. The neglect of scattered radiation can lead to errors as high as 50% in determining the optical constants for bulk copper. For thin films, the errors are much lower. The influence of surface oxidation during measurements in air and surface features of studied objects on the parameters to be determined is analyzed as well. It is shown that errors in determination of the constants are maximal in the plasma resonance region of copper.

     

Optical properties of Cr/Fe(t)/MgO (0 0 1) thin films

In this work we report on the optical properties of single-crystalline iron thin films. For this, Cr-capped Fe films with thickness, t, in the range 30–300 Å were prepared on MgO (0 0 1) by DC magnetron sputtering, and then studied by optical absorption technique within the range from 1.0 to 3.6 eV. All measurements were carried out at room temperature using a fiber optics spectrophotometer. The intensity of the transmitted light decreases with increasing film thickness. The optical constants of the films are deduced from a model that considers the transmission of light by two absorbing films on an absorbing substrate. The absorption coefficient of the Fe films is also calculated from the transmission data. The absorption spectra show the following characteristics: (i) two large absorption peaks centered at about 1.20 and 2.65 eV; and (ii) a sharp step near 1.40 eV. These structures are associated with conventional interband transitions of the iron film.     

MathCAD在椭圆偏振仪测定薄膜光学常数中的应用

薄膜光学常数决定薄膜的光学性能。通过对椭圆偏振仪测试原理的分析,得到求解薄膜光学常数超越方程的数值算法简化公式,并利用MathCAD的“Solve Block”模块开发了基于Windows系统的椭圆偏振测量薄膜光学常数的计算程序,该程序可用于单层有吸收薄膜或无吸收薄膜折射率和厚度的计算。实际应用结果表明,该计算具有数值准确、精度高、运算速度快、适应性好,对系统无特殊要求等优点,可用于薄膜制备过程的在线检测。     

Influence of annealing on the structure formation and optical absorption parameters of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl) acetonitrile thin films

The effect of annealing temperatures (343 and 425) K on structure formation and optical absorption of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films has been reported. The structural properties are investigated by X-ray diffraction and transmission electron microscope techniques. The electronic transitions of DOPNA thin films are investigated in terms of ultravioletvisible (UV-vis) spectroscopy. The absorption coefficient of films has been calculated and analyzed in order to determine the type of inter-band electronic transition as well as the value of optical band gap for films. The films have been found to have indirect allowed optical band gap: which was found to decrease by increasing annealing temperatures.     

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.     

Nanostructured tungsten oxide thin films by the reactive pulsed laser deposition technique

Preparation of nanostructured tungsten oxide thin films using the reactive pulsed laser ablation technique is reported. The structural, morphological, optical and electrical properties of deposited films are systematically studied by changing the ambient oxygen pressure (pO₂). Structural dependence of tungsten oxide films on ambient oxygen pressure is discussed using grazing incidence X-ray diffraction (GIXRD) and micro-Raman spectra. The section analysis using atomic force microscopy exposed the smooth surface features of the deposited films. The blue shift in optical bandgap with an increase in ambient oxygen pressure is expounded in terms of electronic band structure of tungsten oxide. The influence of oxygen pressure on optical constants like extinction coefficient, band edge sharpness, refractive index and optical bandgap is also conveyed. The temperature variation of electrical resistance for films deposited at 0.12 mbar furnishes evidence for its semiconducting nature. PACS 68.55-a; 72.80.Ga; 81.15.Fg; 81.07.Bc; 78.68.+m; 78.20.Ci     

CuO薄膜的三阶非线性光学特性研究

采用脉冲激光沉积技术在Si(100)和熔石英基片上制备了单相的CuO薄膜.通过X射线衍射仪,拉曼光谱仪,场发射扫描电镜和紫外可见光光度计对薄膜的结构,表面形貌和光学性质进行了表征. 场发射扫描电镜结果表明CuO薄膜中晶粒排列致密且分布均匀,其尺寸约为45nm.结合飞秒激光(800nm,50fs)和Z扫描方法测量了薄膜的三阶非线性光学特性,结果表明CuO薄膜具有超快的非线性光学响应且非线性折射率和非线性吸收系数均为负值,其大小分别为-3.96×10^-17 m^{2< 关键词： CuO薄膜 Z-扫描')" href="#">Z-扫描 三阶光学非线性}     

Spectroscopic ellipsometry investigations of PLT ferroelectric thin films with various La concentrations in the mid-infrared spectral region

(Pb_1-xLa_x)Ti_1-x/4O₃ (PLT) ferroelectric thin films with various La concentrations have been grown on LaNiO₃/Si(100) substrates by a modified sol-gel technique. X-ray-diffraction analyses show that the PLT and LaNiO₃ thin films are polycrystalline and entirely perovskite phase. The infrared optical properties of the PLT thin films have been investigated using infrared spectroscopic ellipsometry in the wavelength range of 2.5–12.5 m. By fitting the measured ellipsometric parameter (cos and cos) data with a four-phase model (air/PLT/LaNiO₃/Si), and a derived dispersion relation for the PLT thin films, the optical constants and thicknesses of the thin films have been determined. The refractive index of the PLT thin films decreases with increasing wavelength; however, by a Kramers–Kronig analysis the extinction coefficient increases with increasing wavelength. Moreover, the refractive index and extinction coefficient of the PLT thin films increase with increasing La concentration. This indicates that the infrared optical constants of the PLT thin films are a function of the La concentration. It is believed that the increase in the infrared optical constants of the PLT thin films with increasing La concentration is mainly due to the crystallinity and the electronic band structure of the PLT thin films. PACS 77.55.+f; 78.66.-w; 78.30.Am; 81.70.Fy     

Preparation and characterization of thermally evaporated titanium phthalocyanine dichloride thin films

Titanium phthalocyanine dichloride (TiPcCl₂) thin films are prepared on glass substrates by vacuum-sublimation technique. The optical constants of thin films are obtained by means of thin film spectrophotometry. Planar structures for the study of electrical properties are fabricated with TiPcCl₂ as active layer and silver as the contact electrodes. The effects of post-deposition annealing on the optical band gap have been studied. The optical transition is found to be direct allowed in nature. The invariance in the optical band gap shows the thermal stability of the material. The activation energies are determined using the Arrhenius plots between electrical conductivity and inverse temperature. The variation in activation energy with post-deposition annealing is investigated. The unit cell dimensions of TiPcCl₂ thin films are also determined by indexing the powder diffraction data. The variations of the surface morphology and grain size with annealing have also been studied.     

La掺杂浓度对PLZT薄膜红外光学性质的影响

采用溶胶-凝胶法在Pt/Ti/SiO2/Si衬底上制备了不同La掺杂浓度PLZT(x/40/60)薄膜- x射线衍射分析表明制备的PLZT(x/40/60)薄膜是具有单一钙钛矿结构的多晶薄膜- 通过红外椭圆偏振光谱仪测量了波长为2-5—12-6μm范围内PLZT薄膜的椭偏光谱，采用经典色 散模型拟合获得PLZT薄膜的红外光学常数，同时也拟合获得PLZT薄膜的厚度- 随着La掺杂浓 度的增大，折射率逐渐减小- 而消光系数除PLZT(4/40/60)薄膜外，呈现逐渐增大的趋势- 分析表明这些差异主要与PLZ 关键词： PLZT薄膜 红外光学性质 红外椭圆偏振光谱     

Determination of layer thickness and optical constants of thin films by using a modified pattern search method

We propose the use of a pattern search optimization technique in combination with a seed preprocessing procedure to determine the optical constants and thickness of thin films using only the transmittance spectra. The approach is quite flexible, straightforward to implement, and efficient in reaching the best fitting. We demonstrate the effectiveness of the method in extracting optical constants, even when the films are not displaying interference fringes. Comparison to a real-coded genetic algorithm shows that the modified pattern search is fast, almost accurate, and does not need any parameter adjustments. The approach is successfully applied to extract the thickness and optical constants of spray pyrolyzed nanocrystalline CdO thin films.